BOTH ANTEROMEDIAL AND ANTEROVENTRAL THALAMIC LESIONS IMPAIR RADIAL-MAZE LEARNING IN RATS

Disruption to the anterior thalamus (AT) may be an important factor in diencephalic amnesia. Rats with small lesions of the anteromedial (AM ) or anteroventral (AV) nucleus showed persistent working-memory and r eference-memory deficits in a 12-arm radial maze, although they were c omparable to controls during the early part of training. The only acti vity difference in the maze was that lesioned rats failed to run more slowly when revisiting a baited arm. For all groups, both working and reference memory were impaired after extramaze cues were removed; remo val of intramaze cues further impaired performance relative to the ori ginal conditions. These findings suggest the AT makes a distinct contr ibution to mnemonic functions, probably as part of an integrated syste m involving limbic cortex and the hippocampal formation, and that AT l esions produce a general rather than a specific deficit in spatial or working memory.