Anticipation of an approaching bar by neuronal populations in awake monkey V1

摘要

Visual motion integration in area V1 is traditionally investigated with local stimuli drifting over many cycles within a fixed aperture. However, psychophysical studies have suggested that motion signals can be optimally integrated along the trajectory of a single, translating dot. High detection performance can be explained by the propagation of information between adjacent detector units (Verghese et al., 1999). Such propagation mechanism was proposed to take place within the retinotopic cortical map in area V1 where each local input along the trajectory will elicit a spread of activity that can pre-activate future locations. To test this hypothesis, we recorded single-unit responses (n=80 cells) in area V1 of 2 fixating monkeys when presented with a small bar (4?°) always drifting along the same direction (rightward, 6.6?°/s) but with three different trajectory lengths (1.5, 3 and 6?°). We found in 47% of the neurons an anticipatory build-up of spiking activity for long motion paths, starting as far as 2-4?° from the RF center. This activity was not due to eye movements and was abolished when the order of the stimulus sequence was randomized. To probe the origin of such anticipatory responses, we recorded both LFP signals using multi-electrode-arrays and sub-threshold synaptic activity using voltage-sensitive-dye-imaging (VSDI). LFP responses showed a very early anticipatory signal that could be attributed to a fast feedback signal from higher areas. The dynamics of VSD sub-threshold anticipatory responses matched the spatiotemporal properties of the horizontal connectivity underlying propagation of neural activity within V1 retinotopic maps. Thus, anticipatory spiking response in V1 neurons is probably subtended by a combination of intra and inter-cortical signals converging onto V1 cells. These results highlight the complex, predictive integration of visual motion in primate area V1.