Prefrontal cortex activity related to abstract response strategies

Many monkeys adopt abstract response strategies as they learn to map visual symbols to responses by trial and error. According to the repeat-stay strategy, if a symbol repeats from a previous, successful trial, the monkeys should stay with their most recent response choice. According to the change-shift strategy, if the symbol changes, the monkeys should shift to a different choice. We recorded the activity of prefrontal cortex neurons while monkeys chose responses according to these two strategies. Many neurons had activity selective for the strategy used. In a subsequent block of trials, the monkeys learned fixed stimulus-response mappings with the same stimuli. Some neurons had activity selective for choosing responses based on fixed mappings, others for choosing based on abstract strategies. These findings indicate that the prefrontal cortex contributes to the implementation of the abstract response strategies that monkeys use during trial-and-error learning

Behavioral recovery after transplantation into a rat model of Huntington's disease: Dependence on anatomical connectivity and extensive postoperative training

Rats were trained to perform a conditioned stimulus–response task known to be sensitive to striatal damage, after which they received unilateral excitotoxic striatal lesions. The subsequent implantation of graft tissue into the lesioned striatum was either immediate (9 days) or substantially delayed (70 days). When retested 14 weeks later, all graft and lesion rats were equally impaired initially and biased their responding toward the ipsilateral side. Graft-associated recovery was evident with repeated postoperative testing, but only in rats that had received transplants 9 days postlesion. It is suggested that this training-dependent, graft-associated recovery is mediated specifically by the restored host–graft connections