RESPONSE FIELDS OF INTRAPARIETAL NEURONS QUANTIFIED WITH MULTIPLE SACCADIC TARGETS

The activity of each of 99 intraparietal neurons was studied in three awake-behaving rhesus monkeys (Macaca mulatta) while subjects performe d 100-900 delayed saccade trials. On each trial, a saccadic target was presented at one location selected randomly from a grid of 441 locati ons spanning 40 degrees of horizontal and vertical visual space. Indiv idual neurons in our population were sensitive to both the direction a nd amplitude of saccades. Response fields, which plotted firing rate a s a function of the horizontal and vertical amplitude of movements for each neuron, were characterized by a Cartesian two-dimensional gaussi an model. The goodness-of-fit of these gaussian models was tested by: (1) comparing observed responses with predicted responses for each mov ement; and (2) by computing the percentage of variance explained by ea ch model. Cartesian Gaussian models provided a good fit to the respons e fields of most neurons. Across our population, the Gaussian fit to t he response field of each neuron accounted for more of the variance in neuronal activity when the data were plotted with regard to the horiz ontal and vertical amplitude of the saccade than when the same data we re plotted with regard to the position of the saccadic target. The Gau ssian functions were used to estimate the eccentricity and spatial tun ing breadth of each neuronal response field. Modal response field radi us was less than 5 degrees, whereas mean response field radius was abo ut 10 degrees. Linear regression analysis demonstrated that response f ield eccentricity accounted for less than 30% of the variance in respo nse field radius. Analysis of the horizontal distribution of response field centers showed an approximately normal distribution around centr al fixation. Most histologically recovered neurons were located on the lateral bank of the intraparietal sulcus, although a small number of saccade-related neurons were recorded from Brodmann's area 5 on the me dial bank of the intraparietal sulcus.