We propose experiments to investigate population coding mechanisms in MT, a primate cortical visual area. There is now substantial evidence that MT neurons collectively encode visual motion, and that this information is accessed, or read out, in behaviors requiring motion detection. However, the nature of this code-the neural representation-is not understood. We will study two fundamental aspects of motion representation in MT.
The first (Aim 1) is direction read-out, the mechanism by which many single-neuron activities are collectively interpreted as a single, overall direction. We will specifically determine whether the population of MT activities is interpreted in terms of the peak activity or in terms of the average activity of the cells. We will also determine whether neuron activities contain information about stimulus speed, or whether this information is constructed during the read-out process. Our second goal (Aim 2) is to understand segmentation mechanisms-how MT activities are grouped and assigned to a given moving object. We will test two basic hypotheses, the first stating that motion signals are perceptually bound, or assigned to the same visual object, when they generate a continuous pool of activity in MT. The second hypothesis is that motion signals are perceptually bound by virtue of synchronous firing in the MT population. We will test our ideas with monkeys trained to observe moving stimuli and report what they see. We will simultaneously measure the activities of MT neurons, and these neural data will be subsequently analyzed en masse with statistical models to find activity patterns that consistently foretell the animals' judgements. These will be the first studies to directly explore the link between distributed MT activity and the perception of visual motion.
| Graupner, Michael; Wallisch, Pascal; Ostojic, Srdjan (2016) Natural Firing Patterns Imply Low Sensitivity of Synaptic Plasticity to Spike Timing Compared with Firing Rate. J Neurosci 36:11238-11258 |
| Xu, Hong; Wallisch, Pascal; Bradley, David C (2014) Spiral motion selective neurons in area MSTd contribute to judgments of heading. J Neurophysiol 111:2332-42 |
| Churchland, Mark M; Yu, Byron M; Cunningham, John P et al. (2010) Stimulus onset quenches neural variability: a widespread cortical phenomenon. Nat Neurosci 13:369-78 |
| Bradley, David C; Goyal, Manu S (2008) Velocity computation in the primate visual system. Nat Rev Neurosci 9:686-95 |
| Rosenberg, Ari; Wallisch, Pascal; Bradley, David C (2008) Responses to direction and transparent motion stimuli in area FST of the macaque. Vis Neurosci 25:187-95 |
| Purushothaman, Gopathy; Scott, Benjamin B; Bradley, David C (2006) An acute method for multielectrode recording from the interior of sulci and other deep brain areas. J Neurosci Methods 153:86-94 |
| Bradley, David C; Mascaro, Massimo; Santhakumar, Satish (2005) A relational database for trial-based behavioral experiments. J Neurosci Methods 141:75-82 |
| Purushothaman, Gopathy; Bradley, David C (2005) Neural population code for fine perceptual decisions in area MT. Nat Neurosci 8:99-106 |
| Born, Richard T; Bradley, David C (2005) Structure and function of visual area MT. Annu Rev Neurosci 28:157-89 |
