CONTRIBUTION OF MEDIAL VERSUS LATERAL TEMPORAL-LOBE STRUCTURES TO HUMAN ODOR IDENTIFICATION

To investigate possible distinct contributions of different temporal-l obe structures to odour identification, the University of Pennsylvania Smell Identification Test was administered monorhinally to seizure-fr ee patients who had undergone one of three types of temporal-lobe rese ction practised in three different institutions for surgical treatment of epilepsy The resections were neocorticectomy (Dublin), selective a mygdalo-hippocampectomy (Zurich), or anterior temporal-lobe resection with encroachment on amygdala and hippocampus (Montreal). Resections, analysed from MRI scans, showed unexpected encroachment on medial stru ctures in most patients of the neocorticectomy groups, and largest amy gdala and hippocampal resections in the amygdalo-hippocampectomy group s. Impaired odour identification was observed in all patient groups, i rrespective of surgical approach, with greatest impairment in the nost ril ipsilateral to the resection. The finding of deficits in all three surgical groups suggests that damage in the anterior temporal area, p erhaps in piriform cortex, is sufficient to disrupt performance on thi s task; it may be that function is disrupted in the medial temporal-lo be region by disconnection when the periamygdaloid area is damaged, ev en when amygdala and hippocampus are left intact. An alternative expla nation for our results is that damage in any one, of these areas disru pts a complex network involving several distinct temporal-lobe structu res.