Patients with bipolar disorder have decreased semantic priming, the results of a preliminary study indicate.
The findings, published in the Journal of Behavior Therapy and Experimental Psychiatry, also suggest that the semantic processing abnormalities are of a different nature to those seen in schizophrenia.
Researchers led by Christina Andreou, from Aristotle University of Thessaloniki in Greece, found a negative correlation between priming performance and length of illness in bipolar disorder patients.
"This finding is in concordance with evidence associating neurocognitive impairment, and more specifically verbal memory impairments, with duration of illness in bipolar disorder," say Andreou et al.
They add: "As priming appears to be unrelated to length of illness in schizophrenia, this finding corroborates the hypothesis that priming abnormalities in bipolar disorder and schizophrenia might have a different pathophysiological substrate."
The study involved 14 remitted patients with bipolar disorder and 12 mentally healthy controls matched for demographic variables. The participants were administered a primed lexical decision task with strongly related (STR), weakly related (WR), or unrelated (UR) prime target pairs. The Scale for Thought, Language and Communication (TLC) was used to assess formal thought disorder.
The team found that controls had a robust and statistically significant priming effect for STR words, at 59.6 ms, while priming for WR words was nonsignificant, at 29.4 ms.
By contrast, bipolar disorder patients had no evidence of priming either for STR or WR words, at 5.6 ms and 0.5 ms, respectively.
The only significant correlation between test performance and clinical variables in bipolar disorder patients was a negative correlation between priming for STR words and length of illness, suggesting a decline with increasing duration of illness. There were no significant correlations between priming magnitude and TLC scores in patients.
The team notes that only one bipolar disorder patient scored greater than zero on the TLC disorganization factor. This patient also had the highest priming for STR words in the patient group, and the second highest priming for WR words, at 158 ms and 66 ms, respectively.
The researchers say that the very low TLC scores in the patient group mean that direct comparison with schizophrenia patients was not possible.
Andreou and team conclude: "Further studies including direct comparison of patients with schizophrenia and bipolar disorder are warranted in order to confirm the postulated differences in semantic processing between the two patient groups, as well as to shed light on the question [of] whether the substrates of formal thought disorder in the two diagnostic entities are different."
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