Asymmetric connectivity between the anterior temporal lobe and the language network.

ABSTRACT

The anterior temporal lobe (ATL) sits at the confluence of auditory, visual, olfactory, transmodal, and limbic processing hierarchies. In keeping with this anatomical heterogeneity, the ATL has been implicated in numerous functional domains, including language, semantic memory, social cognition, and facial identification. One question that has attracted considerable discussion is whether the ATL contains a mosaic of differentially specialized areas or whether it provides a domain-independent amodal hub. In the current study, based on task-free fMRI in right-handed neurologically intact participants, we found that the left lateral ATL is interconnected with hubs of the temporosylvian language network, including the inferior frontal gyrus and middle temporal gyrus of the ipsilateral hemisphere and, to a lesser extent, with homotopic areas of the contralateral hemisphere. In contrast, the right lateral ATL had much weaker functional connectivity with these regions in either hemisphere. Together with evidence that has been gathered in lesion-mapping and event-related neuroimaging studies, this asymmetry of functional connectivity supports the inclusion of the left ATL within the language network, a relationship that had been overlooked by classic aphasiology. The asymmetric domain selectivity for language of the left ATL, together with the absence of such an affiliation in the right ATL, is inconsistent with a strict definition of domain-independent amodal functionality in this region of the brain.