Event-related potential study of dynamic neural mechanisms of semantic organizational strategies in verbal learning.

Neuroimaging and neuropsychological data indicate that the frontal regions are implicated in semantic organizational strategies in verbal learning. Whereas these approaches tend to adopt a localizationist view, we used event-related potentials (ERPs) to investigate the dynamic neural mechanisms involved in these strategies. We recorded ERPs using a 128-channel system in 12 young adults (23.75+/-3.02 years) during 3 encoding conditions that manipulated the levels of semantic organization demands. In the Unrelated condition, the words to encode did not share any semantic attributes. For both Spontaneous and Guided conditions, the words in each list were drawn from four semantic categories. In the Spontaneous condition, participants were not informed about the semantic relationship between items. In contrast, in the Guided condition, participants were instructed to improve their subsequent recall by mentally regrouping related items with the aid of category labels. Results indicated that the P200 amplitude increased with the greater organizational demand of semantic strategies. In contrast, the late positive component (LPC) amplitude was larger in both encoding conditions with semantic related words regardless of their instructions as compared to the Unrelated condition. Finally, there was greater right frontal sustained activity in the Spontaneous condition than in the Unrelated condition. Thus, our data indicate that the P200 is sensitive to attentional processes that increase with the organizational semantic demand. The LPC indexes associative processes voluntarily involved in linking related items together. Finally, the right frontal region appears to play an important role in the self-initiation of semantic organizational strategies.