Changes in retention of a visual discrimination task following unilateral and bilateral transections of temporo-entorhinal connections in rats.

In a previous study, it was shown that the lateral entorhinal cortex (LEC) in the left hemisphere contains higher concentration of glutamate than in the right hemisphere. The purpose of the present study was to examine potential relationship between this neurochemical asymmetry and behavior. Rats with either left, right, or bilateral transections of the fiber connections between the temporal cortex and LEC were tested for postoperative retention of a visual discrimination task. Because histological verification of lesions was crucial in this study, analyses of neurochemistry had to be omitted. The results showed that both left and bilateral lesions resulted in impaired retention, but the bilateral group was even more impaired than the left group. The rats with lesions in the right hemisphere, however, used fewer trials to reach the learning criterion than the control group, but they did not make fewer errors than the controls. The results are discussed in terms of lateralization of mnemonic processes.