Disconnection between Rat’s Left and Right Hemisphere Impairs Short-Term Memory but Not Long-Term Memory

Abstract

Split-brain experiments, which have been actively conducted since the twentieth century, have provided a great deal of insight into functional asymmetry and inter-hemispheric interactions. However, how communication between the left and right hemispheres directly contributes to memory formation is still poorly understood. To address this issue, we cut the rat commissural fibers prior to performing behavioral tests, which consisted of two short-term and two long-term memory tasks. The result showed that cutting the commissural fibers impairs short-term memory but not long-term memory. This suggests that the left-right hemispheric interaction through the commissural fibers contributes to the appropriate formation of short-term memory, but not that of long-term memory. Our findings would help to elucidate dynamic memory formation between the two hemispheres and contribute to the development of therapeutics for some neurological diseases which cause a reduction in the inter-hemispheric interaction.

Paradoxical Enhancement of Spatial Learning Induced by Right Hippocampal Lesion in Rats

“…In rodents, in our previous work, we reported that lesions of the rat right hippocampus impaired short-term memory, while lesions of the left hippocampus impaired long-term memory [55]. We also reported results indicating that interhemispheric connections are necessary in short-term memory, but not in long-term memory, suggesting the existence of interhemispheric interactions [63]. Furthermore, according to the elegant experimental results by Shipton et al, "the optogenetic silencing of the left Cornu Ammonis 3 (CA3) alone impaired performance in the hippocampus-dependent long-term memory task, while the unilateral silencing of either the left or right CA3 caused short-term memory deficit in hippocampus-dependent tasks [58,64]" [63].…”

“…The rats were individually housed in cages with free access to food and water under a light-dark cycle, with the light period between 08:00 and 20:00 h. The rats were randomly assigned to the sham group, the right lesion group, the left lesion group, and the bilateral lesion group. All experiments were performed in accordance with the Guidelines for Animal Experiments at Doshisha University and with the approval of the Animal Research Committee of Doshisha University (approval code: A21007) [63].…”

“…All rats were allowed to recover for 7 days and were handled for 5 min each day. They were housed individually to prevent injuries at the surgical site by aggressive behavior between cage mates [63].…”

“…For this test, the T-maze was used as the experimental apparatus. It was made of transparent acrylic plates and comprised three arms that were each 75 cm long, 10 cm wide, and 40 cm high [63]. Prior to this test, habituation was conducted for 30 min per day for 2 consecutive days.…”

“…In rats with impaired learning, the accuracy is expected to be decreased. All procedures in this experiment were performed based on our previous study [63].…”