Shape and Spatial Distribution of Receptive Fields and Antagonistic Motion Surrounds in the Middle Temporal Area (V5) of the Macaque

Abstract

The spatial organization of receptive fields in the middle temporal (MT) area of anaesthetized and paralysed macaque monkeys was studied. In all, 288 neurons were successfully recorded. The size and shape of the receptive field (RF) was mapped with small patches of translating random dots and the resulting data were fitted with a generalized Gaussian. Results show that the RF area increases with eccentricity, and is larger in lamina 5 than in other layers. Most of these RFs are elongated, and the axis of elongation tends to be orthogonal to the preferred direction of motion. The direction selectivity is maintained in all positions in the RF, but layer 5 cells are less direction-selective than cells in other layers. In a second series of experiments, radial dimensions of the classical RF and the antagonistic surround were estimated from area summation tests. These data were fitted with the difference of the integrals of two Gaussians. Surrounds were weakest in layer 4 and strongest in layer 2. Optimal stimulus diameters, also estimated from the area summation curve, were larger in the infragranular layers than in the other layers. The maximum sensitivity of the surround was clearly displaced from the classical RF (CRF) centre, indicating that the surround is not concentric with the CRF. This radial offset and the extent of the surround were largest in layers 2 and 5 and smallest in 3a. The extent of the surround half-height equalled, on average, 3-4 times that of the CRF. These results suggest that antagonistic surrounds are constructed in MT, probably through horizontal connections, and that a strong vertical organization exists in area MT, as has been shown for V1.

Motion detection, noise reduction, texture suppression, and contour enhancement by spatiotemporal Gabor filters with surround inhibition

“…As a result, the suppression will be minimal when the surround stimuli move in opposite direction as compared to the stimulus in the center. This aspect of our model corresponds to neurophysiological findings concluding that surround stimuli with the same direction and speed as the optimal CRF stimulus have a larger suppressive effect on the response of a motion selective neuron than stimuli of other directions and speed of motion (Allman et al 1985;Raiguel et al 1995;Bradley and Anderson 1998). Our model (of V1 cells) also bears a certain resemblance to MT cells, for which the efficacy of center-surround interactions is increased by opposite motion directions.…”

“…However, there are also neurons in V1 and V2, called grating cells, that show selective responses to oriented texture (von der Heydt et al 1991(von der Heydt et al , 1992du Buf 2007,Kruizinga andPetkov 1999). Furthermore, there are cells in MT, called wide-field neurons, that prefer large moving texture fields and exhibit no surround inhibition (Allman et al 1985;Born and Tootell 1992;Raiguel et al 1995). Our model is not aimed at reflecting the properties of these types of neurons, nor of neurons in the MT or MST in general.…”

“…The response of such a neuron is suppressed when moving stimuli are presented in the region surrounding its CRF. The suppression is maximal when the surround stimuli move in the same direction and at the same disparity as the preferred center stimulus (Allman et al 1985;Born and Bradley 2005;Bradley and Anderson 1998;Raiguel et al 1995). In addition, neurons with facilitative surround struc-tures have also been found (Allman et al 1985;Born and Tootell 1992;Raiguel et al 1995).…”

“…The suppression is maximal when the surround stimuli move in the same direction and at the same disparity as the preferred center stimulus (Allman et al 1985;Born and Bradley 2005;Bradley and Anderson 1998;Raiguel et al 1995). In addition, neurons with facilitative surround struc-tures have also been found (Allman et al 1985;Born and Tootell 1992;Raiguel et al 1995). Such neurons show an increased response when motion is presented to their surround and are found in locations that are anatomically different from the ones that have antagonistic surrounds (Born and Tootell 1992).…”

“…A further aim of the current work is to explore some functional aspects of surround suppression in motion processing using a computational model. Surround interactions are observed in different cortical regions such as V1 Jones et al 2001, middle temporal (MT/V5) (Allman et al 1985;Raiguel et al 1995) and lateral medial superior temporal (MST) (Eifuku and Wurtz 1998), which are areas involved in processing motion information. Also, it is known that the RFs of about one half of the cells in MT have antagonistic surrounds (Allman et al 1985;Tanaka et al 1986;Raiguel et al1995;Bradley and Anderson 1998;Born 2000;DeAngelis and Uka 2003;Born and Bradley 2005).…”