Psychological Medicine

Original Articles

Learning and memory in monozygotic twins discordant for schizophrenia

Terry E. Goldberga1 c1, E. Fuller Torreya1, James M. Golda1, J. Daniel Raglanda1, Llewellyn B. Bigelowa1 and Daniel R. Weinbergera1

a1 Clinical Brain Disorders Branch, Intramural Research Program, National Institute of Mental Health, Neuroscience Center at Saint Elizabeths, Washington, DC, USA

Abstract

Learning and memory were assessed in 24 monozygotic (MZ) pairs of individuals discordant for schizophrenia or delusional disorder and seven normal pairs of MZ twins. On declarative memory tasks, the affected group displayed a pattern that might best be characterized as dysmnesic in that they performed significantly worse than the discordant unaffected group on story recall, paired associated learning, and visual recall of designs, but they learned over time, had relatively preserved recognition memory, and did not show profoundly accelerated rates of forgetting. Effortful, volitional retrieval from the lexicon, measured by verbal fluency, was also compromised in the affected group. On the other hand, procedural learning of the motor skill in a pursuit rotor task was relatively intact in the affected group. Comparisons of the normal group and unaffected group indicated that the latter group had very mild impairments in some aspects of episodic memory, namely, immediate and delayed recall of stories and delayed recall of designs. It is highly unlikely that the impairments observed in the affected group can be attributed to differences in genome, family environment, socioeconomic circumstance, or educational opportunity, as all of these were controlled by the twin paradigm. Rather, the impairments appear to be related to the intercession of disease. The neuropsychological profile is consistent with frontal lobe and medial temporal lobe dysfunction, as noted in this sample as well as other samples of schizophrenic singletons. Significant correlations between many measures of memory and global level of social and vocational functioning within the discordant group were also found. Thus difficulties in rapidly acquiring new information and propitiously retrieving old information may burden patients with schizophrenia in many of the transactions of everyday life.

Correspondence:

c1 Address for correspondence: Dr Terry E. Goldberg, Clinical Brain Disorders Branch, Intramural Research Program, National Institute of Mental Health, Neuroscience Center at Saint Elizabeths, 2700 Martin Luther King Jr. Avenue, SE, Washington, DC 20032, USA.

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