Abstracts

Rationale: Retrieving proper nouns (e.g., names of people and places) is a fundamental human ability that depends on the left anterior temporal lobe (ATL). As such, this ability is often impaired in patients with left temporal lobe epilepsy and after resection of the left ATL for epilepsy. Moreover, left ATL lesions can be associated with impaired proper naming regardless of modality (i.e. picture or voice). This finding has led to the idea that the left ATL is a modality-independent convergence region for proper naming. Competing hypotheses for how proper name dispositions are organized within the left ATL include proposals for both a single modality-independent (i.e. heteromodal) convergence region and spatially discrete modality-dependent (i.e. unimodal) regions. The purpose of the current study was to test the hypothesis that the left ATL is heteromodal for proper naming. Methods: Three adult males undergoing seizure localization with intracranial electrodes (and dense ATL coverage), performed picture and voice naming tasks. Subjects named 150 unique pictures (presented for 1 s each) and 150 unique voice clips (presented for 1.5 s each) of three presidents (Bill Clinton, George W. Bush, or Barack Obama) and electrocorticographic (ECoG) responses were recorded. Event-related band power (ERBP) was measured for each ATL recording site and compared to fusiform gyrus (FG) and superior temporal gyrus (STG) for picture and voice naming (Fig. 1). To examine the spectral properties of the ATL, the ERBP was plotted as a function of frequency for each area (ATL, FG, and STG; Fig. 2a). Focusing only on frequencies which showed significant responses compared to baseline (see Fig 2a), we tested whether sites on the left ATL were responsive to voice, picture, or both naming tasks (see Fig 2b). Results: Picture naming resulted in an increase in high frequency (>30Hz) power in FG and voice naming resulted in an increase in high frequency power in STG, approximately 200 ms post stimulus onset (Fig. 1 and 2a), reflecting sensory processing of picture and voice stimuli, respectively. Both picture and voice naming resulted in increased low frequency power (14 - 30 Hz) in the left ATL in a later time window, approximately 400 ms after stimulus onset (Fig. 1 and 2a). In the left ATL, 50% of cortical sites exhibited responses to either picture or voice naming and 50% of cortical sites exhibited responses to both picture and voice proper naming. Cortical sites which were responsive during picture naming tended to be on the ventral ATL, and cortical sites responsive during voice naming tended to be on the lateral ATL (Fig. 2b). Conclusions: Our findings provide direct physiologic evidence for graded convergence of visual and auditory inputs in the left ATL, which would support abstract, modality-independent dispositions for proper nouns. The finding of both unimodal and heteromodal sites in the left ATL unifies theories supporting both unimodal and heteromodal proper naming dispositions in the left ATL. These findings should help inform future ECoG-based mapping of the left ATL.