Impairment in long-term retention of preference conditioning in schizophrenia

Schizophrenia illness is characterized by significant impairments in long-term episodic memory, which are associated with hippocampal abnormalities. This study assessed long-term memory for preference conditioning, which is believed to be more strongly based in the basolateral amygdala, to determine whether abnormalities in biological systems supporting long-term memory are specific to the hippocampus or shared across brain regions involved in different types of memory.

Eighteen schizophrenia (SC) and 24 healthy control (HC) subjects, matched on age, sex, and years of education, participated in the study. All subjects completed an implicit preference conditioning task that associated different patterns with different frequencies of reward. Subjects were then tested for their preference for the patterns both immediately after training, and following a 24-hour delay.

Both SC and HC subjects demonstrated a preference for the more frequently rewarded pattern immediately after training. Following a 24-hour delay, HC subjects continued to prefer the more rewarded pattern in contrast to the less rewarded pattern, but SC subjects did not maintain this differentiation.

These data suggest a significant deficit in the ability to maintain stimulus-reward relationships in memory over long delay periods (24 hours) in individuals with schizophrenia. These data are consistent with prior research indicating normal response to emotional stimuli during learning, but impaired long-term memory for the stimuli, and suggest that there may be a common abnormality in biological systems supporting consolidation of long-term memory across multiple types of memory in individuals with schizophrenia.