Limited sparing of function on spatial delayed alternation after two-stage lesions of prefrontal cortex in the rat

Abstract

Adult rats with complete removals of medial prefrontal cortex (MF) either in 1-stage or 2-stages were tested on a spatial delayed alternation task with a 50 day interoperative interval and with specific training during the interoperative interval. There were two groups receiving 2-stage lesions: one group received a complete lesion of MF cortex in one hemisphere at first surgery followed by a comparable lesion in the other hemisphere at second surgery; the second group received a bilateral lesion of the dorsal component of MF cortex at first surgery followed by bilateral removal of the remaining ventral component at second surgery. The animals in both serial lesion groups were imparied relative to sham operated controls, but they were significantly less impaired than animals receiving similar lesions in a single stage. Several conclusions are drawn from these results: (1) significant sparing of function can be demonstrated after complete serial destruction of MF cortex, but the sparing is not complete. (2) the provision of interoperative experience and a prolonged interoperative interval enhances the degree of sparing observed with 2-stage MF removals as it does with serial lesions of other brain areas. (3) equivalent sparing of function was observed with both serial lesion techniques. Thus, it is not necessary that one hemisphere remain undamaged during the interoperative interval; nor is it necessary that any portion of MF cortex be spared bilaterally during the interoperative interval.