Path integration following temporal lobectomy in humans

Path integration, a component of spatial navigation, is the process used to determine position information on the basis of information about distance and direction travelled derived from self-motion cues. Following on from st udies in the animal literature that seem to support the role of the hippoca mpal formation in path integration, this facility was investigated in human s with focal brain lesions. Thirty-three neurosurgical patients (17 left te mporal lobectomy, LTL; 16 right temporal lobectomy, RTL) and 16 controls we re tested on a number of blindfolded tasks designed to investigate path int egration and on a number of additional control tasks (assessing mental rota tion and left-right orientation). In a test of the ability to compute a hom ing vector, the subjects had to return to the start after being led along a route consisting of two distances and one turn. Patients with RTL only wer e impaired at estimating the turn required to return to the start. On a sec ond task, route reproduction was tested by requiring the subjects to reprod uce a route consisting of two distances and one turn; the RTL group only we re also impaired at reproducing the turn, but this impairment did not corre late with the homing vector deficit. There were no group differences on tas ks where subjects were required to reproduce a single distance or a single turn. The results indicate that path integration is impaired in RTL patient s only and suggest that the right temporal lobe plays a role in idiothetic spatial memory. (C) 2001 Elsevier Science Ltd. All rights reserved.