Memory impairments caused by experimental thalamic lesions in monkeys

A series of experiments examined the effects of selective diencephalic lesions upon object recognition in the cynomolgus monkey (Macaca fascicularis). In the first experiment it was found that extensive lesions of the medial thalamus (MT) produced a severe deficit in both relearning the recognition task and subsequently performing with retention intervals longer than 10 sec. Additional experiments showed that more selective lesions in either the anterior medial thalamus (AMT), the posterior medial thalamus (PMT), or the medial mamillary nucleus (MB) only produced mild recognition memory impairments. It is argued that a combination of damage is required to produce the severe memory impairments observed in cases of global diencephalic amnesia.