Neurocognitive functioning in bipolar disorder

Connectomic signatures of working memory deficits in depression, mania, and euthymic states of bipolar disorder

BACKGROUND

Working memory (WM) deficit is a feature persistently reported across mania, depression, and euthymic periods of bipolar disorder (BD). WM capacity relates to distributed brain regions that are systemically organized at the connectome level. It is not clear whether the same disruption of this network-level organization underlies the WM impairment seen in different phases of BD.

METHODS

We used graph theory to examine the topology of the functional connectome in different granularity in 143 subjects (72 with BD [32 depression; 15 mania; 25 euthymic] and 71 healthy controls) during a n-back task. Linear regression analysis was used to test associations of altered graph properties, clinical symptoms, and WM accuracy in patients.

RESULTS

Altered topological properties characterised by an increase in small-worldness of the whole-brain connectome, were specific for bipolar depressed, but not in manic and euthymic states. Depressed subjects showed a shift in the distribution of the number of connections per brain region (degree) within the connectome during WM task. Increased small-worldness related to worse WM accuracy in patients with more severe depression, anxiety and illness burden.

LIMITATIONS

We used only 2-back load, limiting our ability to study the parametric effects of task demand.

CONCLUSIONS

We demonstrate a putative state-dependent mechanistic link between connectome topology, hub re-distribution and impaired n-back performance in bipolar disorder. The aberrant task-dependent modulation of the connectome relates to worse WM performance especially when anxiety and depression are prominent in BD.

The Bipolar Prodrome: Meta-Analysis of Symptom Prevalence Prior to Initial or Recurrent Mood Episodes

OBJECTIVE

The aim of this study was to meta-analyze the prevalence of symptoms before an initial mood episode of bipolar disorder (BD) and the prevalence of subthreshold symptoms before a BD mood episode recurrence, to facilitate early identification and prevention.

METHOD

Systematic literature reviews were conducted in PsycINFO and PubMed for prospective or retrospective studies reporting on the prevalence and longest duration of symptoms before an initial or recurrent mood episode of BD. Random effects meta-regression explored whether geographic location, age, percentage of female individuals, and study quality moderated the overall prevalence.

RESULTS

In 11 studies (n = 1,078), the prodrome preceding an initial mood episode lasted 27.1 ± 23.1 months (range, 4.6-130 months). In 10 studies (n = 1,000), the subthreshold symptoms preceding a recurrent mood episode lasted 1.0 ± 0.9 months (range, 0.5-1.3 months). The most common symptoms were largely consistent with diagnostic criteria symptoms associated with the subsequent mood polarity for both the initial prodrome and the period prior to a recurrent mood episode. Few moderators of symptom prevalences emerged, and significant heterogeneity remained.

CONCLUSION

The initial prodromal period is sufficiently long and characterized by symptoms of the subsequent mood episode to make early identification and intervention programs feasible. Conversely, the period of subthreshold symptoms before a recurrent mood episode is short, mandating adequate psychoeducation of patients and families, monitoring of changes in sleep and activity, plus sufficiently frequent follow-up visits to identify patients before a mood episode recurrence. Future prospective investigations, designed to address the identified shortcomings in the extant literature, are needed to identify more clinically applicable information.

Dysregulated nitric oxide signaling as a candidate mechanism of fragile X syndrome and other neuropsychiatric disorders

A mechanistic understanding of the pathophysiology underpinning psychiatric disorders is essential for the development of targeted molecular therapies. For fragile X syndrome (FXS), recent mechanistic studies have been focused on the metabotropic glutamate receptor (mGluR) signaling pathway. This line of research has led to the discovery of promising candidate drugs currently undergoing various phases of clinical trial, and represents a model of how biological insights can inform therapeutic strategies in neurodevelopmental disorders. Although mGluR signaling is a key mechanism at which targeted treatments can be directed, it is likely to be one of many mechanisms contributing to FXS. A more complete understanding of the molecular and neural underpinnings of the disorder is expected to inform additional therapeutic strategies. Alterations in the assembly of neural circuits in the neocortex have been recently implicated in genetic studies of autism and schizophrenia, and may also contribute to FXS. In this review, we explore dysregulated nitric oxide signaling in the developing neocortex as a novel candidate mechanism of FXS. This possibility stems from our previous work demonstrating that neuronal nitric oxide synthase 1 (NOS1 or nNOS) is regulated by the FXS protein FMRP in the mid-fetal human neocortex. Remarkably, in the mid-late fetal and early postnatal neocortex of human FXS patients, NOS1 expression is severely diminished. Given the role of nitric oxide in diverse neural processes, including synaptic development and plasticity, the loss of NOS1 in FXS may contribute to the etiology of the disorder. Here, we outline the genetic and neurobiological data that implicate neocortical dysfunction in FXS, review the evidence supporting dysregulated nitric oxide signaling in the developing FXS neocortex and its contribution to the disorder, and discuss the implications for targeting nitric oxide signaling in the treatment of FXS and other psychiatric illnesses.

Cognitive dysfunction is worse among pediatric patients with bipolar disorder Type I than Type II

BACKGROUND

  Impaired profiles of neurocognitive function have been consistently demonstrated among pediatric patients with bipolar disorder (BD), and may aid in the identification of endophenotypes across subtypes of the disorder. This study aims to determine phenotypic cognitive profiles of patients with BD Type I and II.

METHODS

  Subjects (N = 79) consisted of BD I (n = 27) and BD II (n = 19) patients and demographic and intellectually matched healthy controls (HC; n = 33) that completed a battery of neurocognitive tasks.

RESULTS

  Bipolar disorder Type I patients performed significantly more poorly compared to HC on all domains of cognitive function including attention, executive function, working memory, visual memory, and verbal learning and memory. BD I patients also performed more poorly compared to BD II patients on all domains of cognitive functioning with the exception of working memory, whereas BD II patients did poorly relative to HC only on verbal learning and memory.

CONCLUSIONS

  Findings from the current study indicate that BD I patients are characterized by more severe cognitive impairment relative to BD II patients who show an intermediate pattern of performance between BD I patients and HC. Verbal learning and memory may effectively differentiate pediatric BD patients and controls, regardless of the subtype of BD, and may serve as a cognitive endophenotype for the disorder. Additionally, these findings move us closer to developing effective cognitive interventions tailored to specific subtypes of pediatric BD patients.

Executive functioning in familial bipolar I disorder patients and their unaffected relatives

OBJECTIVE

To compare the executive function of patients with familial bipolar I disorder (BP-I) with a history of psychotic symptoms to their first-degree relatives and normal controls.

METHODS

Three domains of executive function: response inhibition, working memory, and cognitive set shifting were assessed in 44 familial patients with a lifetime diagnosis of BP-I who had experienced psychotic symptoms, 42 of their unaffected first-degree relatives, and 47 controls.

RESULTS

Bipolar disorder patients and their unaffected relatives had significantly worse scores for response inhibition compared to healthy controls. The groups did not differ in working memory or cognitive set shifting.

CONCLUSIONS

Impairments in response inhibition are associated with both psychotic bipolar disorder and genetic liability for this illness. Our results indicate that deficits in this specific domain of executive functioning are a promising candidate endophenotype for psychotic bipolar disorder.