PET ACTIVATION OF POSTERIOR TEMPORAL REGIONS DURING AUDITORY WORD PRESENTATION AND VERB GENERATION

Previous studies using positron emission tomography (PET) report blood flow changes in superior and middle temple gyri associated with audit ory and language tasks (Petersen et al., 1988, 1989; Wise et al., 1991 ; Demonet et al., 1992; Howard et al., 1992; Sergent et al., 1992; Zat orre et al., 1992; Petrides et al., 1993; Raichle et al., 1994; Fiez e t al., 1995). An important issue is whether these changes reflect the activation of a single functional region or multiple regions with dist inct functional contributions. In the present study, we examined this issue by focusing upon two tasks for which we have previously reported posterior temporal blood flow changes: listening to auditorily presen ted words (Petersen et al., 1988, 1989), and generation of a verb in r esponse to a visually presented noun (Raichle ct al., 1994); see also Wise ct al. (1991). We began by further characterizing a left temporop arietal region of change previously associated with auditory word pres entation. This previously reported response was replicated, and the re sults were extended by demonstrating presentation of pseudowords also produced activation. We next asked whether the activation associated w ith auditory word presentation could be distinguished from that associ ated with the generation of verbs in response to visually presented no uns. It was found that the activations associated with these two tasks could be both functionally and spatially dissociated. Thus, two poste rior temporal areas associated with auditory word presentation and ver b generation appear to represent distinct areas concerned with word pr ocessing. More generally, the results demonstrate an approach for asse ssing the independence of two activated areas.