One hundred and fifteen male albino rats were used to evaluate 24-h retention of a passive avoidance task following low-level brain stimulation applied during original learning but not during retention. Since the amygdala, substantia nigra, and prefrontal cortex send their afferents through lateral hypothalamus-medial forebrain bundle (MFB), and they have been previously implicated in brain stimulation disruption of memory, the anterior, middle, and posterior portions of the MFB were stimulated. Statistically significant retention deficits relative to operated controls were observed. No impairment in original learning was detected between stimulated animals and operated controls. The disruptive effects of MFB stimulation on retention may be related to the disorganizing influence of the electrical stimulation on amygdaloid, nigro-neostriatal, and frontal cortical fiber systems normally involved in processes leading to retention of this passive avoidance response.
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