Stuck in time without a nucleus: theoretical comment on Sangha et Al. (2005)

Is forgetting caused by the passage of time or by interference from new learning? S. Sangha et al. (2005) offer strong support for the latter idea by using the sea snail Lymnaea. Memory for inhibitory avoidance was prolonged from 3 days to 7 days by preventing the snails from making unreinforced conditioned responses (extinction) following training. Similar effects were obtained with posttraining ablation of the soma of the right pedal dorsal 1, the neuron necessary for consolidation, reconsolidation, and extinction in this task. Without the soma, Lymnaea was unable to retain any new learning or forget old learning, hence remaining "stuck in time." These findings elegantly demonstrate that transcriptional regulation of gene expression is essential for memory consolidation: Local protein synthesis is not sufficient. Furthermore, memory for conditioning and extinction can coexist in the same neuron.