Racing and crowded thoughts in mood disorders: A data-oriented theoretical reappraisal

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Racing and crowded thoughts in mood disorders: A

data-oriented theoretical reappraisal

Gilles Bertschy, Sebastien Weibel, Anne Giersch, Luisa Weiner

To cite this version:

Gilles Bertschy, Sebastien Weibel, Anne Giersch, Luisa Weiner. Racing and crowded thoughts in

mood disorders: A data-oriented theoretical reappraisal. L’Encéphale, Elsevier Masson, 2020, 46 (3),

pp.202-208. �10.1016/j.encep.2020.01.007�. �hal-02935003�

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Review of the literature

Racing and crowded thoughts in mood disorders: A data-oriented

theoretical reappraisal

Tachypsychie dans les troubles de l’humeur : une réévaluation théorique basée sur

les données de la littérature

G. Bertschy

a,b,c,∗

_{, S. Weibel}

a,b

_{, A. Giersch}

b

_{, L. Weiner}

a,d,e

a _{Pôle de psychiatrie, santé mentale & addictologie des hôpitaux universitaires de Strasbourg, 67000 Strasbourg, France} b _{Inserm U1114, 67000 Strasbourg, France}

c _{Fédération de médecine translationnelle de Strasbourg, université de Strasbourg, 67000 Strasbourg, France} d _{Laboratoire de psychologie des cognitions, 67000 Strasbourg, France}

e _{Faculté de psychologie, université de Strasbourg, 67000 Strasbourg, France}

a r t i c l e i n f o

a b s t r a c t

Article history: Received 5 October 2019 Accepted 23 January 2020 Available online 6 March 2020

Keywords: Racing thoughts Crowded thoughts Bipolar Depression Mood disorders

Objectives. – Speed of thought is a central phenomenon in mood disorders. We aimed to provide an update on the topic ten years after a ﬁrst narrative review published on racing and crowded thoughts in mood disorders. This update is based on recent publications, including recent works of our group.

Methods. – Narrative review based on publications from the last ten years including publications of our group and a systematic research of references on PubMed.

Results. – The traditional dichotomist view of racing versus crowded thoughts is not refuted but appears to be more complex, as revealed by validation studies of the Racing and Crowded Thoughts Questionnaire. Moreover, this dualistic view can no longer be conceptualized in a simple bijective concordance with the distinction of hypomania versus mixed depression. We also show that racing/crowded thoughts are strongly associated with mixed depression and not with non-mixed depression, that they tend to be more associated in hypomania to irritability than to the typical symptoms of energy and activity increase and that they are clearly distinguishable from ruminations. Yet, although tightly linked to mood disorders, racing/crowded thoughts appear to be associated to anxiety as well as attention deﬁcit/hyperactivity disorder and insomnia.

Conclusions. – Racing and crowded thoughts should be studied in a dimensional perspective as an important facet of mind activity within and beyond the ﬁeld of mood disorders.

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r é s u m é

Mots clés : Pensées accélérées Pensées grouillantes Tachypsychie Bipolaire Dépression Troubles de l’humeur

Objectifs. – Dix ans plus tôt a été publiée, sous la direction du premier auteur de cet article, une réévaluation théorique sur les pensées accélérées (« racing ») et grouillantes (« crowded ») dans les troubles de l’humeur, que la tradition franc¸ aise rassemble volontiers sous le concept de tachypsychie, mais que les auteurs anglo-saxons utilisent peu. Cette revue incluait des considérations théoriques sur le concept. Après une décade, qui a été marquée par l’émergence du concept de dépression mixte, nous proposons une mise à jour, basée sur les publications récentes incluant des travaux récents de notre groupe.

Méthode. – Cette revue narrative s’appuie sur la réévaluation théorique initiale publiée en 2010 et reprend les publications de ces dix dernières années. Les études pertinentes ont été collectées au ﬁl des travaux de notre groupe, incluent des publications de notre groupe et ont été complétées par une recherche systématique sur PubMed.

∗ Corresponding author at: Hôpital civil, clinique de psychiatrie, 1, place de l’Hôpital, BP 426, 67091 Strasbourg, France. E-mail address: [email protected] (G. Bertschy).

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Résultats. – Nous confirmons les éléments connus sur la tachypsychie en les étendant et en apportant cer- taines clarifications. La conception dichotomique des pensées accélérées versus les pensées grouillantes n’est pas réfutée mais elle apparaît plus complexe, comme l’a révélé les études de validation du Racing and Crowded Thoughts Questionnaire (le questionnaire de pensées accélérées et grouillantes), réalisées chez des sujets de la population générale et chez des patients bipolaires. Ces études montrent, à travers l’analyse factorielle des items composant cet auto-questionnaire, l’existence non pas de deux mais de trois facteurs. Un premier facteur décrit la suractivité des pensées, est associé à l’hypomanie et renvoie assez bien au concept de pensées accélérées linéaires, alors qu’un second facteur décrit le caractère pénible de la suractivité des pensées, est associé à l’humeur dépressive et renvoie, lui, assez bien au concept de pensées grouillantes. Il existe, cependant, un troisième facteur décrivant la surexcitabilité des pensées qui est à la fois associée à l’hypomanie et la dépression et qui vient donc brouiller les cartes du schéma dichotomique. De plus, cette vision dichotomique ne peut plus être conç ue comme dans une simple concordance bijective avec la distinction hypomanie versus dépression mixte telle qu’elle était décrite dans le modèle proposé il y a dix ans. Il semble raisonnable de considérer que, dans la manie sévère, la tachypsychie n’est plus linéaire mais devient grouillante parce qu’à un certain stade, l’accélération excessive des pensées submerge les capacités de traitement de ces pensées par l’esprit. Par ailleurs, les études de la tachypsychie chez des patients déprimés, montrent que celle-ci est fortement associée à la dépression mixte et non à la dépression non mixte. Des études, sur sa présence au cours d’épisodes hypomanes, montrent que la tachypsychie tend à être plus associée à l’irritabilité qu’aux symptômes maniaques classiques d’augmentation de l’énergie et de l’activité. Ces résultats confortent l’intuition de Kraepelin et Weygandt d’un modèle à trois volets des symptômes cliniques des troubles de l’humeur dans lequel pensée associative et activité psychomotrice constituent deux volets distincts (en plus du troisième volet qui concerne les affects). Les travaux récents ont permis aussi d’apporter des éléments empiriques pour étayer la distinction entre tachypsychie et ruminations. Enfin, bien qu’étroitement liée aux troubles de l’humeur, la tachypsychie semble être associée à l’anxiété aussi bien dans la population générale que chez les sujets bipolaires. Elle est également très présente chez les sujets présentant un trouble déficit de l’attention/hyperactivité ou souffrant d’insomnie.

Conclusion. – La tachypsychie, telle qu’elle s’exprime par des pensées accélérées et grouillantes, représente un concept clinique qui permet d’étudier une importante facette de l’activité de l’esprit dans une perspective dimensionnelle dans et au-delà du domaine des troubles de l’humeur.

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1. Introduction

Racing thoughts refer to a subjective acceleration and overproduction of thoughts, which have been essentially associated with manic episodes in bipolar disorder. Indeed, racing thoughts, and their verbal equivalent, flight of ideas, are extremely characteristic, if not pathognomonic, of manic thinking [1]. As Jamison so vividly described it [2], manic thought is characterized by “[. . .] a torrent of near unstoppable speech; thoughts bracchiate from topic to topic, held only by a thin thread of discernible association. Ideas fly out, and as they do, they rhyme, pun, and assemble in unexampled ways. The mind is alive, electric.” In his groundwork textbook on bipolar disorder, Kraepelin [3] was the first to use the term “flight of ideas”, to refer interchangeably to both the experience of speeded thought pressure, and its expression in the patient’s speech. Kraepelin conception of racing thought was strongly linked to his conception of mixed state he developed with his student Weygandt [4]. They described three distinct areas of psychic functioning: affect, psychomotor activity and associative thinking that could be excited or depressed, independently from the others. This resulted into eight combinations, including six mixed states (in addition to the two states of either homogenous excitation/mania or homogenous depression). Among them, two mixed states combined excited associative thinking and depressed affect.

The term “racing thoughts” appeared in the American classification of the Diagnostic and Statistical Manual for Mental Disorders third edition in 1980 [5], but only in the criterion B3 of mania: “flight of ideas or subjective experience that thoughts are racing”. Since then, the wording has stayed the same. It became the criterion B4 in the DSM-III-R [6], and in the DSM-IV [7]. The Text- revision version of DSM-IV [8] gives a more specific description: “The individual’s thoughts may race, often at a rate faster than

can be articulated”, “This experience resembles watching two or three television programs simultaneously.” The flight of ideas is described by a logorrhea (which is also considered by itself in the criterion B3), with abrupt changing of topics, such that the speech can be disorganized and incoherent. The ICD-10, the WHO classification published in1994 [9], considers only the flight of ideas in the manic episode with psychotic symptoms.

Although racing thoughts have been abundantly described by psychiatrists, it is still unknown whether they belong to a single entity, or are rather a multi-faceted phenomenon. The clinical boundaries and characteristics of racing thoughts have not been thoroughly evaluated in patients with mood disorders. There are reasons to believe that racing thoughts might be associated not only with full-blown manic, but also with depressive episodes in bipolar disorder. As mentioned above, Kraepelin [3] had already suggested that depression “with flight of ideas” and other mixed typolo- gies of depression were common occurrences of mood episodes in manic-depressive illness. However, when racing thoughts co-occur with depressive mood, instead of conveying a sense of speed and flow, associated with pleasant emotions, thoughts are described as numerous and “overcrowded” in the patient’s head, and are associated with unpleasant emotions [10–12]. Thus, phenomenologically speaking, although the term “racing thoughts” reflect an unitary concept, racing thoughts might consist of at least two kinds of thought activity – “racing” and “crowded”, associated with manic and depressed mood, respectively. For instance, Benazzi [12] described crowded thoughts as “continuous flooding of the mind by ideas that the person could not stop” and racing thoughts as “increased speed of thinking”.

In 2010, a theoretical reappraisal of the phenomenology of racing and crowded thought in mood disorders [13] was published under the direction of one of us (GB). We propose here, a decade

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later, an update on this narrative review based on new empirical data that has called into question the dichotomist view of racing vs. crowded thoughts found in hypomania and mixed depression, respectively. To do so, we will follow the plan of the initial theoretical review (for convenience sake we will call it the 2010 review). For each section, we will do a short synthesis of the 2010 review and then integrate the contribution of studies published since then, including the contributions of our group. References have been col- lected downstream during the 10 last years of research activity of our group and they have been completed by a prospection on Pubmed database using the following query: (“racing”[All Fields] or “crowded”[All Fields]) and (“thought”[All Fields] or “thoughts”[All Fields])).

2. Evolution of the concept and of the phenomenological perspectives

The introduction section of this paper summarized the evolution of the concept until 2010. Since the 2010 review [13], the fifth edition of the DSM was published in 2013 [14]. However, it did not modify the wording of the B4 criterion for mania used in the preceding version (“Flight of ideas or subjective experience that thoughts are racing.”). An important evolution is that the DSM-5 [14] fully acknowledges that racing thoughts could be associated to a depressive syndrome, coining the term “depression with mixed features” to refer to the co-occurrence of subsyndromal manic symptoms in depressive episodes. This is a real advance even if the stringent criteria exposes to a high risk of underdiagnosis of mixed depression [15]. The ICD-11, the new version of the WHO classification published online in 2018 [16], has included rapid and racing thoughts in its description of hypomanic episodes whereas flight of ideas is associated to the description of a manic episode even in the absence of psychotic symptoms. The universality of racing thoughts as a symptom of mania has been recently illustrated in a paper about the concept of mania in traditional Andean culture [17]. Noteworthy is also the publication in 2018 of a validation study of the Koukopou- los Mixed Depression Rating Scale, a new mixed mood rating scale [18]. “Racing and crowded thoughts” is one of the 14 items of the scale. The instructions for its rating are the following: “This symptom is of cardinal importance. Note spontaneous reports before direct questioning. Rate on the basis of subjective experience that thoughts/memories are more than usual, and/or thinking is accel- erated. Depressive ruminations are different: they are made up by few (often only one) depressive preoccupation.”

During the last decade, few phenomenological studies have focused on racing and crowded thoughts. In a qualitative analysis of audiotaped interviews exploring subjective experience of thought overactivation in patients with mood disorders, our research group described five conceptual categories which characterized thought overactivation: sequential thought flow (i.e., one thought leading to another), overstimulation, competition for resource allocation, unexpected/unexplained onset of thoughts, and association with mood and emotions [19]. In the same paper [19], a principal component analysis of a newly developed 16-item auto-questionnaire to study thought overactivation indicated that a single component explained 55.9% of the variance with major and exclusive contributions from 9 items. This single major component did not support a dualistic view of racing thought versus crowded thought and suggested instead that subjective thought overactivation encompasses an overproduction of thoughts but also thoughts getting muddled, as well as the unrestrained/uncontrollable nature of thought flow. These characteristics echo the ones revealed by the qualitative analysis: thoughts are perceived as unexpected, too easily triggered, difficult to inhibit and competing for resource allocation [19]. Thus, consistent with phenomenological accounts of racing thoughts,

these qualitative findings suggested that racing thoughts was a multi-faceted concept [19]. To address the multi-faceted nature of racing and crowded thoughts which were not targeted by this early scale [19], our group developed a 34-item self-rating scale, the Rac- ing and Crowded Thoughts Questionnaire (RCTQ) assessing thought overactivity during the past 24 hour. Some of its items were related to the phenomenology of racing thoughts and refers to increased thought velocity [e.g. “My thoughts race much too fast”), sequential and easy unfolding (e.g. “There is a succession of thoughts in my mind, racing from one to the other with incredible ease”). Some items were related to the phenomenology of crowded thoughts referring to an increased amount of simultaneous thoughts (e.g. “I have too many thoughts at the same time”). Others were related to the negative consequences of thought overactivation (e.g. “My brain cannot manage all these thoughts that arise at the same time” or “My mental overactivity is exhausting”). Items were rated on Likert scale ranging from zero (“not at all”) to four (“completely agree”). We first investigated its psychometric properties in healthy subjects [20]. Indeed, recent studies in healthy individuals have reported racing thoughts in the unaffected offspring of patients with bipolar disorder [21], have suggested that racing thoughts might be present in healthy undergraduate students [22] and young adults reported their thoughts as more racing than older adults [23]. Exploratory factor analysis of the RCTQ in healthy individuals [20] yielded a three-factor solution, labeled “thought overactivation”, “burden of thought overactivation”, and “thought overexcitability”. The “thought overactivation” subscale was selectively associated with current elated mood and included items conveying both the notion of increased amount and velocity of thoughts which echoed the concept of racing thoughts in hypomania, whereas the “burden of thought overactivation” subscale was associated with current low mood and its content echoed the concept of crowded thoughts. The “thought overexcitability” subscale included items conveying the notion of distractibility, and, in contrast with the first two factors, was associated with both elated and low mood. Subsequently, in a large clinical study including French, Italian and Belgian bipolar patients led by our group [24], the three-factor solution of the RCTQ yielded the best fit indices when compared with a single factor model proposed by our initial work [19] or an hypotheti- cal two-factor model based on the racing versus crowded thought distinction. The short 13-item RCTQ, resulting from the removal of redundant and less discriminant items within the three factors, had the strongest psychometric properties [24].

The identification of racing and crowded thoughts in clinical practice is particularly difficult, hence highlighting the need of a specific instrument targeting this symptom. In a study of patients seeking treatment for anxiety or mood symptoms and substance use symptoms, comparison of racing thoughts as endorsed by the patient when fulfilling the Mood Disorder Questionnaire [25] and racing thoughts as identified by the psychiatrists using the MDQ as a semi-structured interview, resulted in a low agreement score (kappa = 0.15). Similar results were found for irritability and distractibility symptoms, whereas excessive spending, increased goal-directed activity and hypersexuality reached higher agreement scores [26].

3. Prevalence of racing/crowded thoughts in mood disorders

The aforementioned 2010 review [13] had put forward the synthesis published by Goodwin and Jamison in their 2007 book [1] and reported other original studies published afterwards whose results were in agreement with Goodwin and Jamison’s results. Based on 12 studies, Goodwin and Jamison [1] found that the mean prevalence of “ﬂight of ideas/racing thoughts” in mania/hypomania

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was 76%, with a 41 to 100% range. To our knowledge, there are no recent studies with data about the prevalence of racing thoughts in hypomania or mania.

The prevalence of racing thought/crowded thoughts in depressed patients was not addressed in Goodwin and Jamison’s book [1]. The 2010 review [13] described data issued from original studies: the prevalence range was large in depressed patients; from 5 to more than 50%. Such differences did not seem clearly related to the distinction bipolar versus unipolar depression and seemed to be related to methodological differences that were also highly correlated to authors’ specific interest. Benazzi’s huge personal contribution to the field of mixed depression and the unipolar/bipolar depression distinction is a good illustration of this point [27]. The number of studies published during the last decade and provid- ing data about the prevalence of racing/crowded thoughts during a depressive episode is in sharp contrast with the lack of equivalent studies in the field of mania: it reflects the growing research about mixed depression. We review below these recent studies about the prevalence of racing/crowded thoughts in depression.

In the NIMH Collaborative Depression Study, the prevalence of racing thoughts/flight of ideas during bipolar major depressive episodes was 7.7% [28]. In the Systematic Treatment Enhance- ment Program for Bipolar Disorder, the prevalence of “racing thoughts/flight of ideas” in bipolar patients [29] was 17% in those with a major depressive episode and 30% in those with a DSM-IV mixed episode (which required that both the criteria of a major depressive episode and of a manic episode were fulfilled) [7]. In a study of the International Mood Network, in an international mixed sample of bipolar and unipolar patients with a major depressive episode, the global prevalence rate of racing or crowded thoughts was 25% and when the sample was split between patient fulfilling and not fulfilling the Koukopoulos criteria for mixed depression the prevalence rates of racing and crowded thoughts was respectively 46 and 4% in the two subsamples [30]. The 46% rate is close to the 48% rate of mixed depressive patients using the same Koukopou- los criteria found by the same author in a cohort of Italian patients [31]. It is noteworthy that in this study racing and crowded thoughts were not related to nor triggered by ongoing antidepressant treatment [31]. In the BRIDGE study, based on a sample of depressed patients, the prevalence of racing thoughts was 11.8% whereas it was 59.9% in the subsample of patients fulfilling DSM-5 criteria for depressive mixed states and 62.3% in the subsample of patients fulfilling the study specific Research-Based-Diagnostic-Criteria for depressive mixed states [32]. When a cluster approach was used with the BRIDGE study data, it distinguished a first cluster of non- mixed depression and a second cluster of mixed depression: the prevalence of racing thoughts was respectively 3.9 and 34.4% in the two clusters [33]. Yet, when clinical features predicting cluster label were identified using a stepwise logistic regression model, racing thoughts was not one of the seven symptoms that best predicted cluster membership [33]. In the BRIDGE study, the prevalence of racing thoughts, as for most hypomanic symptoms, was higher in patients with a more recurrent depressive disorder: 12.1% in subjects with more than 3 lifetime episodes versus 7.4% with patients with 3 or less episodes [34], a difference that is mainly linked to the positive association between recurrence and markers of bipolar disorder. In the same BRIDGE study, what has been found for recurrent depression was also observed for borderline personality disorder: a positive association with markers of bipolar disorder and a higher prevalence of racing thoughts when a borderline personality disorder is present (30.5 versus 10.5%) [35]. In a Japanese sample of major depressive episode patients, the prevalence of flight of ideas/racing thoughts was 36.4%, and it was lower in the subgroup of major depressive disorder patients (20.0%) than in the subgroup of bipolar II/bipolar not otherwise specified patients (58.7%) [36]. In a Brazilian study [37], the prevalence of racing thoughts during the

worst lifetime depressive episode was higher in men (19.5%) than in women (14.6%), and higher in atypical or agitated subtypes compared to melancholic subtypes. The link between racing thoughts during depression and bipolar spectrum conditions was also supported by a study in depressed youth [38], showing an increased odds ratio for racing thoughts in depressed youth with high familial risk for bipolar disorder compared to those with low familial risk; subsyndromal hypomanic symptoms, particularly motor hyperactivity, distractibility, and flight of ideas/racing thoughts, were higher in bipolar depressed youth, and discriminated bipolar depressed from unipolar depressed youth. Finally, one study conducted during a pharmacological trial included patients (from USA and Eastern Europe) with mixed depression as defined by a major depressive episode with two or three hypomanic symptoms (excluding distractibility, irritable mood and psychomotor agitation): the prevalence of the DSM-5 symptom of “flight of ideas or racing thoughts” was 66.8% [39]. It is noteworthy that in this study, “flight of ideas or racing thoughts” was the manic symptom with the highest prevalence (preceding “more talkative or pressure to keep talking” and “distractibility” with respective prevalence at 61.1 and 59.2%) [39], whereas in others studies with patients with major depression with and without mixed features it was not the case [28,30,32,36]. In conclusion, recent studies suggest a 30 to 70% prevalence of racing/crowded thoughts in mixed depression, much higher than a 4 to 12% prevalence in non-mixed depression. More- over, the presence of racing/crowded thoughts is clearly associated with the bipolar spectrum.

It is also interesting to mention a study about the phenomenology of pre-(hypo)manic and pre-depressed prodromal symptoms [40]: “racing thoughts” is the second more frequent symptoms occurring before the first (hypo)manic episode with a prevalence of 78.6%, behind “feeling extremely energetic” (85.7%) and before” physical agitation” (76.2%). In the same vein, the association of “racing thoughts” to “elation” or “irritability” in general population probands who did not meet full criteria for hypomania or mania at study intake, was a significant predictor of a first episode of hypomania or mania during the next three years [41]. These results echo those from a study of the treatment of bipolar depression

[42] whereby the relationship between manic items and treatment

emergent mania was explored using a factor analysis to identify cluster of manic symptoms that covaried. Four factors were identi- ﬁed, but the motor/verbal activation factor, which included racing thoughts, was the only one signiﬁcantly related to treatment emergent mania.

4. Association of racing/crowded thoughts with other affective symptoms

In the 2010 review [13], studies using principal component analysis, in manic patients showed convergent results: racing thoughts was usually found in a factor including other classical manic symptoms such as elated mood, increased energy, activity, self-esteem and social contact as well as ﬂight of ideas and acceleration of speech. However, one study by Benazzi using the Mood Diagnostic Questionnaire (MDQ), a self-report questionnaire screening past hypomanic or manic episode [25], suggested that racing thoughts was associated with irritability and it was not related to increased energy and activity [43]. In a study of the Brazilian version of the MDQ [44], racing thoughts was the second higher loaded item after irritability on the ﬁrst factor revealed by principal component analysis, a second factor being loaded mainly by “more energy” and “more active”. Such results echo other results which were not included in the 2010 review [13]. In an extended sample, Benazzi [45] found similar results to his aforementioned initial study [43]: factor analysis of hypomanic symptoms during

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hypomanic episodes showed that the “racing/crowded thoughts” item was part of a second factor associated to “irritable mood” and “distractibility” distinct from a more classic ﬁrst factor which included “elevated mood”, “inﬂated self-esteem”, “decreased need to sleep”, “talkativeness” and “overactivity”. In a Honk-Kong validation study of the Mood Diagnostic Questionnaire (MDQ), principal component analysis indicated that “racing thoughts” was included in a “euphoria-irritability-racing thoughts” factor distinct from an “energized-activity” factor, and a “risky behavior” factor [46]. To summarize, recent studies suggest that racing thoughts are more associated with irritability than energy and activity increase. Thus, racing thoughts are related to the “dark” side and not only the “sunny” side of hypomania. This lends some indirect support to Kraepelin and Weygandt’s proposal [4] that mood disorders include three distinct areas of psychic functioning (affect, psychomotor activity and associative thinking) and psychomotor activity and associative thinking may be dissociated in hypomania.

The 2010 review [13] mentioned only one study of hypomanic symptoms in depressed patients using principal component analysis [47]: racing thought appeared in the only hypomanic factor alongside other behavioral hypomanic symptoms such as logorrhea, increased activity and social contact. We have found several recent studies concerning the association of racing thoughts with other symptoms during manic/hypomanic states. For instance, one study reported the association of racing thoughts with other hypomanic symptoms during a depressive episode [48]; an exploratory factor analysis of hypomanic symptoms identiﬁed three factors: factor 1 (“elation-disinhibition-increased goal directed activity”), factor 2 (“risk-taking-impulsivity-substance use”) and factor 3 (distractibility–irritability), racing thoughts was included in this last factor. Of note, in a study of former inpatients who commit- ted suicide [49] – (60% with bipolar disorder, 22% with a major depressive disorder or episode, 7% with a schizoaffective disorders and more than 80% with depression –, at the time of their suicide), racing thoughts were identiﬁed in 53.1% of the patients; such prevalence was lower than the prevalence of suicidal thinking (74.0%) or inner tension (54.2%) but higher than the prevalence of delu- sions (38.5%), aggressive behavior (31.2%) or psychomotor agitation (30.2%). This suggests that racing thoughts could be a mixed-related feature that links depression and risk of suicide [50].

5. Racing/crowded thoughts and other illnesses

The 2010 review [13] stressed that neither the DSM-IV, nor the ICD-10, mentioned the concept of racing thoughts in any other categories of mental disorders. This is not any different from the newly-deﬁned DSM-5 categories [14]. Yet, as mentioned in the 2010 review [13], racing/crowed thoughts are frequently reported by patients presenting with other mental disorders. In anxiety and particularly in panic attacks, racing thoughts are a frequent symptom related to hyperarousal. The 2010 review [13] also reported one study of racing thoughts in borderline incarcerated women

[51] and highlighted the importance of this ﬁnding, given the high

rates of comorbid borderline personality disorders in bipolar disorder. The same applies to attention deficit/hyperactivity disorder (ADHD) [13], although the 2010 review points to the fact that racing thoughts have been predominantly associated with bipolar disorder rather than ADHD. Finally, concerning schizophrenia, the review pointed to the ambiguity linked to the use of the term flight of ideas [13]. Whereas racing thoughts could be considered as the subjective equivalent of the flight of ideas in the field of mood disorders, this is different in schizophrenia. Andreasen [52] used the concept of “derailment” suggesting that it is the loosening of the degree of association between thoughts, not their acceleration that is crucial to flight of ideas in schizophrenia. Derailment

in schizophrenia is a “slow, steady slippage”, whereas in mania “ﬂight of ideas is a derailment that occurs rapidly in the context of pressured speech” [52].

However in her clinical work, Andreasen [53] showed that thought disorders in schizophrenia and mania were qualitatively similar; their severity only varied along a spectrum: schizophrenic and manic thought disorders being respectively the most severe and less severe forms. Consistently, a recent systematic review and meta-analysis of formal thought disorder in schizophrenia and bipolar disorder [54] supported the view that, in the acute inpatient samples, there was no signiﬁcant difference in the severity of positive formal thought disorders between schizophrenia and bipolar disorder patients.

Concerning the question of anxiety, our own studies have confirmed the view developed in the 2010 review [13] that there was a link between racing thoughts and anxiety both in the general population [20] and in mood disorders patients [19,24]. This link could rely on a common dimension of hyperarousal in anxiety states and in hypomanic or mixed bipolar states. Concerning ADHD, preliminary results from our group [55] have shown that RCTQ score was significantly higher in ADHD patients compared to controls and even compared to manic patients. Racing thoughts in ADHD patients were more severe at bedtime and correlated positively with insomnia, and with mood instability, two clinical symptoms highly prevalent in ADHD. Moreover, there is a high rate of association between ADHD and bipolar disorder [56]. Last but not least, we also found that patients with primary insomnia have high RCTQ score, with a predominance of racing thought at bedtime [57]. Thus, racing and crowded thoughts are a phenomenological dimension at the heart of mood disorders but also seem to be at the intersection of other related psychopathological dimensions such as anxiety, arousal, attention and sleep disorders. Finally, in this section, we must include the perspective of comorbidities in bipolar disorder, even if the data are limited. We found a study comparing bipolar disorder in youth with and without high-functioning autism spectrum disorder (HF-ASD): racing thoughts and distractibility were the only two manic symptoms significantly more prevalent at study intake in patients with HF-ASD as compared with patients without HF-ASD [58]. Maybe ADHD which is highly associated with HF-ASD

[59] could contribute to this difference.

6. Racing/crowded thoughts and depressive rumination

The 2010 review [13] proposed, yet without empirical data to support this hypothesis, that in mixed depressive states crowded thoughts should be clearly distinguished from rumination. The authors claimed that patients with rumination seemed able to report the contents of their rumination, contrary to patients with crowded thoughts who were overwhelmed by many ideas with many themes and felt unable to “catch their thoughts” [13].

Our recent studies confirmed the independence of the concept of racing/crowded thought and the concept of rumination by showing no relationship between the RCTQ score and the two subscales scores of the Ruminative Response Scale State version [60] neither in a general population sample [20] nor in a clinical sample [24]. Besides, a French study [61] showed that the level of depression in subjects initially admitted as emergencies for acute anxiety depressive disorders and/or suicide attempts was correlated with increased ‘flow of thoughts’, but not number of thoughts; these two dimensions were elegantly assessed by filling a drawing of an aquarium to reflect the number of thoughts (by drawing fish) and cognitive turmoil (by drawing wavy lines).

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7. Synthesis and perspective for future research

The 2010 review [13] proposed a theoretical model distinguishing racing and crowded thoughts. Racing thoughts in hypomania and mania were conceptualized as linear racing thoughts and the result of an increased production of new thoughts with a normal ability to inhibit previous thoughts. Crowded thoughts in mixed depression were conceptualized as resulting from an increased production of new thoughts, a common process with linear racing thought, associated to a decreased inhibition of previous thoughts, a process that would be common to the ruminations [13]. In other words, crowded thoughts could be a hybrid of racing thoughts and ruminations. In 2012, Desseilles et al. [62] proposed a slightly more complex perspective based on a three, rather than two, dimensional model of thoughts in mood disorders: to the dimension of thought quantity and emotional valence of thought, they added the dimension of thought associative pattern which could be characterized as narrow or broad. In the current review, we propose an approach slightly different from the 2010. Linear racing thoughts could be limited to hypomanic states whereas, as already described by Goodwin and Jamison [1], in severe manic and in mixed manic states, rapid thinking proceeds to fragmented and disjointed thinking phenomenologically closer to crowded thoughts as reported in mixed depression. This perspective does not abandon one of the key proposals of the previous model whereby racing thoughts become crowded thoughts due to an imbalance between the emergence of new thoughts in consciousness and the cognitive ability to grasp them, acknowledge them and put them aside to pass to the next. In mixed depression, this disequilibrium arises from the increase of new thoughts linked to the hypomanic psychic excitation and the difficulty to discard negative thought linked to the depressive ruminative process. In hypomania or moderate mania, the cognitive ability to treat new thought parallels the acceleration of thoughts production. By contrast, in more severe manic states, the cognitive ability to treat new thoughts is overwhelmed by an excessive acceleration of thought production. This mirrors another well-known clinical aspect [1,3]: the inverse U-shaped relationship of the level of productivity/creativity and the severity of hypomania/mania. This perspective of a reduction of cognitive productivity with increasing severity of manic symptoms is supported by our study [63] showing that “thought overexcitability”, one of the three factors of the Racing Crowded Thought Question- naire (RCTQ), was linked to decreased verbal output in certain task conditions assessing verbal fluency. Moreover, from a neu- ropsychological perspective as well, the same study [63] showed that the ability to switch from one word to another in verbal fluency tasks, akin to racing thoughts, differentiated the mixed depression group from typical depression, suggesting that very few activation symptoms concurrent with depression might give rise to speech and thought abnormalities similar to those found in mania.

There are other perspectives that have not been explored during the last decade and remained to be studied. One of them is how the flow of time is experienced: in mania time is more often experienced as flowing quickly [64]. Our preliminary results [65] revealed that in controls, elevated rates of racing thoughts measured via the RCTQ were associated with the feeling that time passed fast, but in patients racing thoughts and time perception tasks were not correlated. Another perspective concerns the emergence in the field of mind-wandering of the concept of intentionality: intentional and unintentional mind-wandering seems to be dissociable [66]. Although racing and crowded thoughts are intuitively considered as an unintentional and often overwhelming phenomenon, the mind-wandering literature raises the question of whether some forms of linear racing thoughts might be intentional. Experimen- tal manipulations that accelerate thought also yield positive affect,

hence suggesting that it is possible to experimentally induce the phenomenon of linear racing thoughts [67].

8. Conclusion

There has been ten years since the publication of our initial theoretical reappraisal focusing on the phenomenology of racing and crowded thoughts [13]. During this decade, mixed depression has become a major research interest in the ﬁeld of mood disorders, and so has the focus on racing thoughts as a possible distinguishing symptom between mixed and non-mixed types of depression. This makes this update on this key symptom all the more needed.

The present paper conﬁrms and extends the understanding of racing and crowded thoughts. The dichotomist view of racing versus crowded thoughts, although not refuted, seems to be more complex than initially conceptualized, as it does not fully reﬂect the distinction between hypomania and mixed depression. Studies published during the last decade have also shown that racing/crowded thoughts are strongly associated with mixed depression as compared with non-mixed depression, and that, in hypomania, they are more associated with irritability than with the typical symptoms of energy and activity increase, on the one hand, and that they are distinct from rumination, on the other hand. Yet, although central to mood disorders, racing/crowded thoughts appear to be associated with anxiety as well as ADHD and insomnia. Racing and crowded thoughts should thus be viewed in a dimensional perspective, as an important facet of mind activity within and beyond mood disorders. Given its good psychometric properties, our newly developed self-report questionnaire, the Racing and Crowded Thoughts Questionnaire [20], may be a reliable means of clinically assessing this important and frequent symptom.

Disclosure of interest

The authors declare that they have no competing interest.

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