Funding Amount: $224,479

Abstract: DESCRIPTION (provided by applicant): Visual motion signals in extrastriate visual area MT provide the primary sensory input that guides smooth pursuit eye movements. Because of the broad tuning of MT neurons for target direction and speed, many neurons are active in MT when a target moves with any given direction and speed: as a consequence, any given visual motion is represented in the brain by the discharge of a large population of neurons, called the "population response". The long-term goal of this application is to understand how the population response is read by the motor system to provide commands for smooth pursuit eye movements. Prior work has allowed us to form the hypothesis that target speed is decoded from the population response in MT by performing a vector-averaging computation on an opponent motion signal, where the computation is biased toward estimating low speeds if the population response is noisy or has a low amplitude. We now will ask how target direction is coded and decoded for pursuit. Direction has been chosen for analysis because it offers advantages for understanding how the decoding computation is done with neurons. We will develop an analysis that is based on the mean and variation of individual neural and behavioral responses in awake, trained rhesus monkeys. We will conduct behavioral experiments to determine how well pursuit can discriminate between targets moving in slightly different directions, for stimuli with and without directional noise. We will record the mean and variation of neural responses in MT during the directional discrimination, and investigate co-variation of neural and behavioral responses as well as correlations between the responses of pairs of MT neurons. Then, we will evaluate possible neural mechanisms for decoding target direction by computer simulations of a neural network model with a realistic population code and neuraly plausible decoding mechanisms. Our proposed approach investigates the situation faced by the pursuit system in real life, when it must estimate target direction on the basis of individual responses of many neurons. It will provide us an understanding of the neural operations performed in neural circuits between the cerebral cortex and cerebellum, shedding light on the normal functions of pathways that are compromised in many strokes and motor disorders and potentially leading to new therapies for assisting in recovery from strokes.

Thesaurus Terms:

neural information processing, neuroregulation, sensory discrimination, smooth pursuit eye movement, visual perception, visual tracking computer data analysis, computer simulation, information system, motor neuron, neural transmission, neurophysiology, neuropsychology, sensorimotor system, time resolved data, visual stimulus Macaca mulatta, behavioral /social science research tag, electrode, oscillography, single cell analysis

Funding Amount: $316,056

Abstract: DESCRIPTION (provided by applicant): Smooth pursuit eye movements in primates provide an accessible example of motor behavior guided by sensory inputs. Pursuit movements are controlled by cortical representations of target motion and access some of the same higher cortical regions implicated in planning and decision making. In preliminary work we have shown that pursuit behavior is variable but surprisingly precise, that the variability has a simple structure, and that it can be attributed mainly to errors in sensory estimates of target motion parameters. The surprisingly precise relationship between eye trajectories and target motion is established over time windows of 100 ms durations. Thus, pursuit gives us a remarkable situation - a genuine primate sensory-motor behavior in which the input-output relationship is computational simple, while relevant time scales are short enough that each cell can contribute at most a few spikes. Thus, in the equation in which behavior is a function of neural activity, both sides are much simpler than might have been expected. The potentially combinatorial complexity involved in a complete analysis of the neural code itself and the connection between spike trains and behavior is dramatically simplified. We propose 1) to understand the neural codes for sensory and motor signals at multiple levels of the neural circuit for pursuit, 2) to correlate the activity of single cortical, brainstem and cerebellar neurons with the trial-to-trial variability of motor output in awake, behaving animals, and 3) to bridge the gap from what we can measure (co-variation of neural and behavioral responses in single trials) to what we want to know (architecture and signal processing in the full sensory-motor circuit). The outcome of this line of research will be an understanding of how multiple cortical and sub-cortical areas work together to generate a single kind of voluntary movement. It will have direct impact on how we understand neurological disorders of movement, and on the consequences of disruptions or enhancements of correlations between neurons. Correlations and neuronal oscillations are an important feature of normal motor function, and this project will help us to understand how to understand their malfunctions and to design behavioral therapies to mitigate their disruption in epilepsy, nystagmus, and movement disorders.

Thesaurus Terms:

psychomotor function, smooth pursuit eye movement
biophysics, brain electrical activity, neural information processing, neuroanatomy, synapse, training
Macaca mulatta, behavior test, electrode, mathematics