The cerebellum and cognition: cerebellar lesions do not impair spatial working memory or visual associative learning in monkeys

Anatomical studies in non-human primates have shown that the cerebellum has prominent connections with the dorsal, but not the ventral, visual pathway s of the cerebral cortex. Recently, it has been shown that the dorsolateral prefrontal cortex (DPFC) and cerebellum are interconnected in monkeys. Thi s has been cited in support of the view that the cerebellum may be involved in cognitive functions, e.g. working memory. Six monkeys (Macaca fascicula ris) were therefore trained on a classic test of working memory, the spatia l delayed alternation (SDA) task, and also on a visual concurrent discrimin ation (VCD) task. Excitotoxic lesions were made in the lateral cerebellar n uclei, bilaterally, in three of the animals. When retested after surgery th e lesioned animals were as quick to relearn both tasks as the remaining uno perated animals. However, when the response times (RT) for each task were d irectly compared, on the SDA task the monkeys with cerebellar lesions were relatively slow to decide where to respond. We argue that on the SDA task a nimals can prepare their responses between trials whereas this is not possi ble on the VCD task, and that the cerebellar lesions may disrupt this respo nse preparation. We subsequently made bilateral lesions in the DPFC of the control animals and retested them on the SDA task. These monkeys failed to relearn the task. The results show that, unlike the dorsal prefrontal corte x, the cerebellum is not essential for working memory or the executive proc esses that are necessary for correct performance, though it may contribute to the preparation of responses.