Common and disease-specific dysfunctions of brain systems underlying attentional and executive control in schizophrenia and bipolar disorder

Abstract

Schizophrenia and bipolar disorder broadly overlap in multiple areas involving clinical phenomenology, genetics, and neurobiology. Still, the investigation into specific elementary (sub-)processes of executive functioning may help to define clear points of distinction between these categorical diagnoses to validate the nosological dichotomy and, indirectly, to further elucidate their pathophysiological underpinnings. In the present behavioral study, we sought to separate common from diagnosis-specific deficits in a series of specific elementary sub-functions of executive processing in patients with schizophrenia and bipolar disorder. For our purpose, we administered a modern and multi-purpose neuropsychological task paradigm to equal-sized and matched groups of schizophrenia patients, patients with bipolar disorder, and healthy control subjects. First, schizophrenia patients compared to the bipolar group exhibited a more pronounced deficit in general measures of task performance comprising both response speed and accuracy. Additionally, bipolar patients showed increased advance task preparation, i.e., were better able to compensate for response speed deficits when longer preparation intervals were provided. Set-shifting, on the other hand, was impaired to a similar degree in both patient groups. Finally, schizophrenia patients exhibited a specific deficit in conflict processing (inhibitory control) and the shielding of task-relevant processing from distraction (i.e., attentional maintenance). The present investigation suggests that specific neuropsychological measures of elementary executive functions may represent important points of dissociation between schizophrenia and bipolar disorder, which may help to differentiate the pathophysiological underpinnings of these major psychiatric disorders. In this context, the present findings highlight the measures of inhibitory control and attentional maintenance as promising candidates.

Dysregulation within the Prefronto-Parietal Background-Monitoring Network in Schizophrenia

“…In a previous behavioral study, schizophrenic patients showed a deficit in the shielding of task relevant processing from distracting irrelevant stimulus information, both in conflicting situations and in situations with an irrelevant oddball [31]. The underlying pathophysiological mechanisms of that deficit have not been directly investigated so far, although there are several studies using oddballs [39]- [45] and conflicts in the investigation of neurofunctional changes in schizophrenia [46]- [51].…”

“…In an adapted version of the combined oddball-incongruence task patients with schizophrenia exhibited specific impairments in both oddball and incongruency trials, which might indicate that a common cognitive process, underlying both task, is disrupted rather than a process specific to either oddballs or incongruency. The shielding of task relevant processing from distracting irrelevant stimulus information is necessary to perform in both tasks and it might therefore be concluded that this process is disrupted in that group of patients [31]. But the question, whether this disruption arises due to the same neural mechanism of a heightened sensitivity of the background-monitoring system (or parts of it) to distracting information, remains to be answered.…”

Cortical activation abnormalities in bipolar and schizophrenia patients in a combined oddball–incongruence paradigm

“…Furthermore, it has repeatedly been shown that schizophrenia patients suffer from greater cognitive impairment than bipolar disorder patients [ 40 – 44 ]. Consequently, their compensation mechanisms seem to be more limited than in affective disorders which may explain the missing compensatory activation in frontal brain areas observed in this study.…”

Multimodal Emotion Integration in Bipolar Disorder: An Investigation of Involuntary Cross-Modal Influences between Facial and Prosodic Channels

“…It also possible that the BD-related findings observed here are not specific to emotion, but rather relate to more general difficulties in receiving different information simultaneously. Indeed, it is widely recognized that patients with BD exhibit pervasive deficits in executive functioning that translate to difficulties in shifting between information sources and simultaneously thinking about multiple concepts (McKirdy et al, 2009; Melcher et al, 2013). Such neurocognitive deficits have been shown to underpin unimodal emotion processing in schizophrenia populations (Brekke, Kay, Lee, & Green, 2005), and it is certainly possible that our results reflect the downstream outcome of this cognitive inflexibility.…”