THE ROLES OF SEMANTIC NETWORKS AND SEARCH EFFICIENCY IN VERBAL FLUENCY PERFORMANCE IN INTRACTABLE TEMPORAL-LOBE EPILEPSY

Two competing hypotheses (i.e., disruption of semantic networks vs. se arch inefficiency) concerning the mechanisms underlying impaired seman tic verbal fluency in temporal lobe epilepsy (TLE) were tested within a single paradigm. Reports that semantic verbal fluency is more impair ed in left than right TLE groups were confirmed by the findings that t he left TLE group produced fewer words on a supermarket fluency task t han 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 group s. Because both TLE groups generated fewer words per category of super market items sampled, and produced a higher ratio of category labels r elative to category exemplars than did the NC group, it can be surmise d that TLE disrupts semantic memory networks. The findings did not sup port the competing hypothesis that reduced semantic verbal fluency in TLE is a manifestation of inefficient search/retrieval strategies, pos sibly associated with distal frontal lobe pathophysiology. Specificall y, the TLE and NC groups did not differ significantly in their mean nu mber of perseverations, intrusions, or search efficiency (operationali zed as the ratio of the number of shifts between categories to the num ber of categories sampled).