The roles of left versus right anterior temporal lobes in semantic memory: A neuropsychological comparison of post-surgical temporal lobe epilepsy patients

The presence and degree of specialisation between the ATLs is a key issue in debates about the neural architecture of semantic memory. Here, we comprehensively assessed multiple aspects of semantic cognition in a large group of post-surgical TLE patients with left versus right anterior temporal lobectomy (n=41). Both subgroups showed deficits in expressive and receptive verbal semantic tasks, word and object recognition, naming and recognition of famous faces and perception of faces and emotions. Graded differences in performance between the left and right groups were secondary to the overall mild semantic impairment; primarily, left resected TLE patients showed weaker performance on tasks that required naming or accessing semantic information from a written word. Right resected TLE patients were relatively more impaired at recognising famous faces as familiar, although this effect was observed less consistently. These findings unify previous partial, inconsistent results and also align directly with fMRI and transcranial magnetic stimulation results in neurologically intact participants. Taken together, these data support a model in which the two ATLs act as a coupled bilateral system for the representation of semantic knowledge, and in which graded hemispheric specialisations emerge as a consequence of differential connectivity to lateralised speech production and face perception regions.