Supra-second interval timing in bipolar disorder: examining the role of disorder sub-type, mood, and medication status

Abstract

Background : Widely reported by bipolar disorder (BD) patients, cognitive symptoms, including deficits in executive function, memory, attention, and timing are under-studied. Work suggests that individuals with BD show impairments in interval timing tasks, including supra-second, sub-second, and implicit motor timing compared to the neuronormative population. However, how time perception differs within individuals with BD based on BD sub-type (BDI vs II), mood, or antipsychotic medication-use has not been thoroughly investigated. The present work administered a supra-second interval timing task concurrent with electroencephalography (EEG) to patients with BD and a neuronormative comparison group. As this task is known to elicit frontal theta oscillations, signal from the frontal (Fz) lead was analyzed at rest and during the task. Results : Results suggest that individuals with BD show impairments in supra-second interval timing and reduced frontal theta power compared during the task to neuronormative controls. However, within BD sub-groups, neither time perception nor frontal theta differed in accordance with BD sub-type, mood, or antipsychotic medication use. Conclusions : his work suggests that BD sub-type, mood status or antipsychotic medication use does not alter timing profile or frontal theta activity. Together with previous work, these findings point to timing impairments in BD patients across a wide range of modalities and durations indicating that an altered ability to assess the passage of time may be a fundamental cognitive abnormality in BD.

Figure 1.. Propensity histogram for neuronormative control and bipolar patient groups.

Distribution of control (grey) and bipolar (teal) propensity scores along X axis indicates similar distribution of demographic variables for both groups. Nearly all participants have an estimated probability of being in the BD group that is greater than 0.5 because the majority of our sample belongs to the BD group. This graph indicates that while our groups may not be perfectly balanced, the degree of imbalance between them is not indicative of significant sampling bias.

Figure 2.. Individuals with bipolar disorder show impairments in supra-second interval timing and abnormal frontal theta compared to neuronormative controls.

A. Schematic diagram of supra-second interval timing task. Trials begin when participants are shown a 3s or a 12s timing cue. Participants press the spacebar to indicate their estimation of the target interval. B. Response distribution for neuronormative controls vs. individuals with bipolar disorder. C. Individuals with bipolar disorder over-estimate the short interval compared to controls [left]. No differences in response distribution were detected [right]. D. Individuals with bipolar disorder do not differ from controls in estimation of the long interval duration [left], however, individuals with bipolar disorder have a significantly wider response distribution compared to controls [right]. E. Individuals with bipolar disorder show lower theta power compared to individuals in the neuronormative control group during the supra-second interval timing task. Mean and standard error of the mean plotted in bar graphs. Dots represent values from individual subjects. * p < 0.05

Figure 3.. Individuals with bipolar disorder and neuronormative controls do not differ in frontal theta power at rest.

A. To assess resting-state differences in theta power between bipolar disorder and neuronormative control groups resting-state data were analyzed. No differences in resting-state theta power were identified between neuronormative control and bipolar groups. Mean and standard error of the mean plotted in bar graphs. Dots represent values from individual subjects. * p < 0.05

Figure 4.. Interval timing performance and frontal theta power do not differ as a function of bipolar disorder sub-type. A.

Schematic diagram of supra-second interval timing task. Trials begin when participants are shown a 3s or a 12s timing cue. Participants press a button to indicate their estimation of the target interval. B. Response distribution for individuals with bipolar I or bipolar II disorder. C-D. Groups do not differ in time estimation for the short [C] or the long [D] intervals. E. Frontal theta power during the ITT did not differ between groups. Mean and standard error of the mean plotted in bar graphs. Dots represent values from individual subjects. * p < 0.05

Figure 5.. Interval timing performance and frontal theta power do not differ as a function of mood.

A. To assess task-wide differences in oscillatory activity data from the whole interval-timing task were analyzed. B. Response distribution for individuals with bipolar disorder who were either euthymic or depressed at the time of data collection. C-D. Groups do not differ in time estimation for the short [C] or the long [D] intervals. E. Frontal theta power during the ITT did not differ between groups. * p < 0.05

Figure 6.. Interval timing performance and frontal theta power do not differ as a function of antipsychotic medication status.

A. Response distribution for individuals with bipolar disorder divided by anti-psychotic medication status. B-D. Groups do not differ in time estimation for the short [C] or the long [D] intervals. E. Frontal theta power during the ITT did not differ between groups. Mean and standard error of the mean plotted in bar graphs. Dots represent values from individual subjects. * p < 0.05