As a group, patients with schizophrenia perform poorly on a broad range of neuropsychological tasks, particularly those measuring long-term memory, working memory, attention, and executive functioning.[43*] Bipolar patients show similar deficits, however, less pronounced: declarative memory and executive functioning are often impaired even in the euthymic state of bipolar disorder, but abstraction, perceptual motor speed, and vigilance are superior compared with schizophrenic patients;[45*] in a direct comparison, Seidman et al. reported that patients with chronic psychotic bipolar disorder had a generally similar, albeit less severe, pattern of deficits as compared with patients with chronic schizophrenia.
Neuropsychological impairments also characterize vulnerability states. Several recent meta-analyses primarily suggest moderate deficits in verbal memory recall in relatives of schizophrenic patients. Studies[41**,48] on relatives of bipolar patients provide less robust results; the most reliable finding is also impaired memory in relatives of bipolar patients.
Two psychophysiological measures are associated with the term sensory gating. Both, the P50 component of the auditory evoked potential and the startle reflex after intense stimuli, are attenuated when the stimulus evoking the response is briefly preceded by another stimulus; both measures appear to be largely independent of each other. Prepulse inhibition (PPI) as well as P50 gating is reduced in schizophrenic patients and their healthy relatives. Patients with acute mania also have reduced P50 inhibition, particularly if they had a history of psychosis. Thus, impaired sensory gating might reflect a general, diagnostically unrestricted vulnerability to psychosis.
Many studies demonstrate that the amplitude of the auditory P300, which occurs after target detection, is reduced in schizophrenia; the latency is also delayed in the same patients. Similar changes are frequently observed in relatives but the effects are of moderate size and not always consistent. Reports of P300 amplitude reduction and latency increase were observed in bipolar patients and in their relatives as well.
In sum, cognitive impairments, sensory gating, and P300 deviations are less pronounced in bipolar patients but qualitatively similar for the memory domain. Putative medication effects,[55*] however, limit conclusions about specific deficits.
Curr Opin Psychiatry. 2006;19(2):165-170. © 2006 Lippincott Williams & Wilkins
Cite this: Schizophrenia and Bipolar Disorder: Differences and Overlaps - Medscape - Mar 01, 2006.