Bipolar disorder patients perform worse than do their counterparts without-bipolar disorder at language comprehension tests at the behavioral level, but not the physiological level, according to findings from a small-scale study.
A team of researchers from CHU Sainte Marguerite and Aix-Marseille Université, Marseille, France, examined behavioral and electrophysiological responses to speech by measuring the "N400 effect," an ERP (event-related brain potential) observed in patients with bipolar disorder and schizophrenia that typically is provoked via the subjects’ response to unexpected or incongruous words at the end of a sentence.
Led by Dr. Michel Cermolacce of CHU Sainte Marguerite, the team compared responses from 38 participants, including 19 bipolar type I patients and 19 healthy comparison subjects. The patients with bipolar disorder were recruited from the Marseille University Department of Psychiatry while presenting a mild to severe manic episode and did not have concurrent neurological disorders (J. Affect. Disord. 2014;158:161-71).
The participants in the study were asked to listen to a series of congruous and incongruous complete sentences and judge whether the last word of each sentence was congruous or incongruous. The subjects’ brain waves were measured throughout the test with an electroencephalogram.
The study participants with bipolar disorder exhibited a lower rate of correct responses for both congruous endings (76.7%, compared to 80% from healthy subjects) and incongruous endings (75% in patients with bipolar disorder, and 80% from healthy subjects). In addition, bipolar patients had longer response times when looking for congruous endings than their peers did (1,120 ms compared to 970 ms for healthy subjects.)
However, EEG readings showed preserved amplitude but delayed latency in difference waves, suggesting no significant disruption of brain waves through the N400. The authors noted that the findings contrast with the only previous N400 study, which showed a disruption of brain waves that is in line with similar results found in patients with schizophrenia (Prog. Neuropsychopharmacol. Biol. Psychiatry 2012;38:194-200). The previous study used visually presented word pairs rather than verbal word pairs, an approach the authors contend does not reflect a natural language setting.
Dr. Cermolacce and his colleagues cited several limitations, including the study’s small sample size and the absence of a group of patients with schizophrenia.
However, the findings suggest that specificity and adherence to natural speech patterns should be taken into account when examining speech disruptions in patients with mental disorders in a research setting, they noted.
"The discrepancy in manic patients between (i) preserved N400 and (ii) delayed [Late Positive Component] and impaired behavioral performances under natural speech conditions can be interpreted as reflecting non-specific cognitive rather than primary language alterations in line with previous behavioral findings," they wrote.
The authors report no conflict of interest.