Developmental regulation of plasticity in cat somatosensory cortex.

Abstract

1. The neocortical response to deprivation of somatic sensory input in young animals of different ages was compared with the same manipulation in adults. The response was measured through the use of 2-deoxyglucose (2DG) mapping. Although several features of the cortical response were similar in animals of all ages, the metabolic patterns evoked by somatic stimulation differed substantially from each other at all ages. 2. When adult cats receive a digit amputation and survive from 2 to 8 wk, the pattern of stimulus-evoked metabolic uptake expands dramatically in the somatosensory cortex contralateral to the deprived forepaw. Comparisons between the normal and experimental somatosensory cortices reveal that the distribution of activity on the experimental side was roughly an expanded version of the normal pattern. 3. Unilateral digit amputations of digit 2 were conducted on kittens 2, 4, or 6 wk old. They survived until 3-4 mo and then received a 2DG experiment, during which digit 3 was stimulated bilaterally. Evaluation of the evoked metabolic pattern indicated substantial differences from the activity elicited in adults undergoing identical manipulations. 4. The individual patches of activity that made up the metabolic pattern were similar in intensity in both hemispheres when the digit amputation was conducted at either 2, 4, or 6 wk. After a digit amputation at 2 wk, the patches were significantly narrower in the experimental hemisphere; after a digit amputation at 6 wk, the patches were significantly wider in the hemisphere receiving from the deprived forepaw. 5. Two-dimensional maps of 2DG uptake in areas 3b and 1 of the somatosensory cortex reveal that after a digit amputation at 2, 4, or 6 wk, the distribution of activity in the hemisphere receiving from the digit amputation was more dispersed and widespread than in the normal hemisphere. The dispersed pattern of uptake was not an expanded version of the normal pattern, but scattered over a wider region of somatosensory cortex. This observation is similar to the normal pattern of evoked activity seen in developing animals. 6. The total area of 2DG uptake in the somatosensory cortex contralateral to a digit amputation conducted at 2 or 4 wk was not greater than that in the normal hemisphere, even though it was more widespread. After a digit amputation at 6 wk, however, the area of evoked activity was greater in the experimental hemisphere but not of the magnitude as the same manipulation in an adult.(ABSTRACT TRUNCATED AT 400 WORDS)