The roles of semantic networks and search efficiency in verbal fluency performance in intractable temporal lobe epilepsy.

Abstract

Two competing hypotheses (i.e., disruption of semantic networks vs. search inefficiency) concerning the mechanisms underlying impaired semantic verbal fluency in temporal lobe epilepsy (TLE) were tested within a single paradigm. Reports that semantic verbal fluency is more impaired in left than right TLE groups were confirmed by the findings that the left TLE group produced fewer words on a supermarket fluency task than did the normal control (NC) group, and that the performance of the right TLE group was intermediate to that of the left TLE and NC groups. Because both TLE groups generated fewer words per category of supermarket items sampled, and produced a higher ratio of category labels relative to category exemplars than did the NC group, it can be surmised that TLE disrupts semantic memory networks. The findings did not support the competing hypothesis that reduced semantic verbal fluency in TLE is a manifestation of inefficient search/retrieval strategies, possibly associated with distal frontal lobe pathophysiology. Specifically, the TLE and NC groups did not differ significantly in their mean number of perseverations, intrusions, or search efficiency (operationalized as the ratio of the number of shifts between categories to the number of categories sampled).