Rats with either sham operations, small medial frontal cortex lesions (SMF), or large medial frontal cortex lesions (LMF) were tested in the open field, for spatial alternation and for 8-arm maze learning. The behaviors of sham-operated and SMF rats were similar on the spatial learning tasks, while the LMF group performed poorly in relation to these two groups. In contrast, the two lesion groups differed from the sham group, but not from each other, on locomotor activity in the open field. The differences in performance between the SMF and LMF groups on the spatial learning measures suggest that medial frontal cortex lesion size and locus may be important factors underlying the variable results of previous studies evaluating spatially-oriented behaviors of rats with varying degrees of medial frontal cortex damage.

Rats from dams that were undernourished (8% casein diets) during pregnancy and lactation or weH fed (25% casein diets) received frontal corticallesions at maturity. The animals were then tested for the ability to master a simple sensory discrimination and to learn reversals of that discrimination. Main effects of undernutrition and the frontal corticallesion were found in originallearning but not on the reversals, and animals that received both early undernutrition and the later focal brain lesion made more errors in originallearning than did rats that sustained only undernutrition or only the lesion. The suggestion that early nutritional history may be one of a number of factors that can help to explain why patients with seemingly similar brain lesions do not always show identical symptoms is discussed.Subjects who receive lesions of the same brain structures do not always exhibit identical degrees of behavioral impairment (Finger & Stein, 1982). Several factors have now been proposed to account for this variability, which has been observed both with clinical populations and laboratory animals. For example, under some conditions it is known that age at the time of insult can affect the degree of functional sparing (Johnson & Almli, 1978), as can the speed of growth or "momentum" of the lesion (Finger, 1978b). In addition, nonspecific environmental "enrichment" has also been shown to enhance behavioral recovery, at least on simple maze-learning tasks following cortical or hippocampal lesions (Finger, 1978a).A variable that has only recently been explored in this context is the early nutritional history of the sub-[ect. Early undernutrition can affect several indices of brain function, including cellular growth and differentiation and synapse formation and myelination, and it has also been established that some behaviors can be affected if undernutrition is experienced during the period of rapid brain growth (Winick, 1976). These observations may be interpreted to suggest that early undernutrition can also affect recovery from later brain damage-a hypothesis that has now been examined in three recent studies from this laboratory, using the pups of rat dams that had experienced 50010 less food than control dams during the lactation period.The results of two of these studies have shown that early undernutrition can affect performance following a brain lesion later in life, even under conditions in which poor early diet has little or no effect on the scores of rats without focal brain lesions. In one case (Mangold, Bell, Gruenthal, & Finger, 1981), in which rats with posterior corticallesions were tested for the ability to make a brightness discrimination, poor early nutrition retarded recovery following the focal lesion. In the other, in which rats with hippocampal lesions were tested on a battery of DRL operant conditioning tasks, undernutrition attenuated the lesion effect (Finger & Green, 1983). The generality of the latter finding was examined in a third study (Laughlin, Finger, & Bell, 1983) in which rats were...

Rats with an early history of severe malnutrition received frontal cortical (FC) lesions or control operations at 90 days of age. These severely malnourished groups were compared with each other and with moderately malnourished and well-fed groups (FC and control) for acquisition and three reversals of a tactile discrimination (rough-smooth). Main effects of lesion and nutrition were found for acquisition and reversals. The groups with malnutrition plus frontal lesions displayed the poorest performance. Although the severely and moderately malnourished groups did not differ in acquisition of the discrimination, the severely malnourished group made more reversal errors. The severely malnourished rats also showed greater brain growth retardation (size and weight) than the moderately malnourished rats. These results indicate that the effects of early dietary history and the reaction to a later, acute brain injury may be additive under certain circumstances.

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