A NEW VIEW OF HEMINEGLECT BASED ON THE RESPONSE PROPERTIES OF PARIETAL NEURONS

Lesion studies of the parietal cortex have led to a wide range of conc lusions regarding the coordinate reference frame in which hemineglect is expressed. A model of spatial representation in the parietal cortex has recently been developed in which the position of an object is not encoded in a particular frame of reference, but instead involves neur ones computing basis functions of sensory inputs. In this type of repr esentation, a nonlinear sensorimotor transformation of an object is re presented in a population of units having the response properties of n eurones that are observed in the parietal cortex. A simulated lesion i n a basis function representation was found to replicate three of the most important aspects of hemineglect: (i) the model behaved like pari etal patients in line-cancellation and line-bisection experiments; (ii ) the deficit affected multiple frames of reference; and (iii) the def icit could be object-centred. These results support the basis-function hypothesis for spatial representations and provide a testable computa tional theory of hemineglect at the level of single cells.