Internal timing mechanisms disrupted in bipolar disorder patients
MedWire News: Results from a US study suggest that internal mechanisms that control timing are impaired in patients with bipolar disorder.
"Alterations in time perception and neural circuitry associated with internal timing have been found in several neuropsychiatric disorders that share phenomenological and genetic overlap with bipolar disorder, including schizophrenia and attention deficit/hyperactivity disorder," say William Hetrick (Indiana University, Bloomington) and team.
"However, investigations of time perception in bipolar disorder… are scarce," they add.
The team therefore recruited 42 patients with the mood disorder and 42 age-matched healthy controls. Of the patients with bipolar disorder, 25 were euthymic and 17 were experiencing mania at the time of the study.
All of the participants performed a paced finger-tapping task in which they were asked to tap in time with an auditory stimulus (synchronization), and then without auditory help while attempting to maintain the same pace (continuation). This task was performed with the dominant index finger and then with alternate thumbs.
The team also used the Wing-Kristofferson mathematical model to estimate the contribution of internal clock versus motor implementation components in timing variability of inter-response intervals.
The researchers found that participants with bipolar disorder tapped significantly faster than controls in both the synchronization and continuation conditions, with an overall mean intertap interval of 521 versus 530 ms.
Bipolar disorder patients also showed significantly greater variation in intertap intervals to that of controls in both the synchronization and continuation conditions, and with the dominant index finger and alternate thumbs.
There were no significant differences between euthymic and manic bipolar disorder patients regarding finger-tapping task performance.
Using the Wing-Kristofferson model, the team found significantly greater internal clock variability in bipolar disorder patients compared with controls.
However, there were no significant differences between the two groups regarding motor implementation variability.
"Overall, impaired performance on the repetitive-tapping task employed in this study suggests that internal timing mechanisms are disturbed in bipolar disorder," conclude Hetrick and team.
They suggest that "increased clock variability in bipolar disorder may be related to abnormalities in cerebellar function."
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By Mark Cowen