Biology subjects

Sedaghat-Nejad, E.

Publications and source records attributed to Sedaghat-Nejad, E..

2 recordsLinked to original sources

bioRxiv2019

Behavioral training of marmosets and electrophysiological recording from the cerebellum

The common marmoset (Callithrix Jacchus) is a promising new model for study of neurophysiological basis of behavior in primates. Like other primates, it relies on saccadic eye movements to monitor and explore its environment. Previous reports have demonstrated some success in training marmosets to produce goal-directed actions in the laboratory. However, the number of trials per session has been relatively small, thus limiting the utility of marmosets as a model for behavioral and neurophysiological studies. Here, we report the results of a series of new behavioral training and neurophysiological protocols aimed at increasing the number of trials per session while recording from the cerebellum. To improve the training efficacy, we designed a precisely calibrated food regulation regime that motivated the subjects to perform saccade tasks, resulting in about a thousand reward-driven trials on a daily basis. We then developed a multi-channel recording system that used imaging to target a desired region of the cerebellum, allowing for simultaneous isolation of multiple Purkinje cells in the vermis. In this report, we describe (1) the design and surgical implantation of a CT guided, subject specific head-post, (2) the design of a CT and MRI guided alignment tool for trajectory guidance of electrodes mounted on an absolute encoder microdrive, (3) development of a protocol for behavioral training of subjects, and (4) simultaneous recordings from pairs of Purkinje cells during a saccade task.\n\nNew and NoteworthyMarmosets present the opportunity to investigate genetically based neurological disease in primates; in particular, diseases that affect social behaviors, vocal communication, and eye movements. All of these behaviors depend on the integrity of the cerebellum. Here, we present training methods that better motivate the subjects, allowing for improved performance, and also present electrophysiological techniques that precisely target the subjects cerebellum, allowing for simultaneous isolation of multiple Purkinje cells.\n\nIn our parks, are there any trees more elegant and luxurious than the Purkinje cell from the cerebellum? Santiago Ramon y Cajal

neuroscience↗

bioRxiv2019

Reward prediction error modulates saccade vigor

Movements toward rewarding stimuli exhibit greater vigor, i.e., increased velocity and reduced reaction-times. This invigoration may be due to release of dopamine before movement onset. Dopamine release is strongly modulated by reward prediction error (RPE). Here, we generated an RPE event in the milliseconds before movement onset and tested whether there was a causal relationship between RPE and vigor. Human subjects made saccades toward an image. During the execution of their primary saccade, we probabilistically changed the position and content of the image. This led to a secondary saccade following completion of the primary saccade. We focused on properties of this secondary saccade. On some trials, the content of the secondary image was more valuable than the first image, resulting in a +RPE event that preceded the secondary saccade. On other trials, this content was less valuable, resulting in a -RPE event. We found that reaction-time and velocity of the secondary saccade were affected in an orderly fashion by the magnitude and direction of the preceding RPE event: the most vigorous saccades followed the largest +RPE, whereas the least vigorous saccades followed the largest -RPE. Presence of the secondary saccade indicated that the primary saccade had experienced a movement error, inducing trial-to-trial adaptation: the subsequent primary saccade was changed in the direction of the movement error in the previous trial. However, motor learning from error was not affected by the RPE event. Therefore, reward prediction error, and not reward per se, modulated vigor of saccades. Author summaryDoes dopamine release before onset of a movement modulate vigor of the ensuing movement? To test this hypothesis, we relied on the fact that RPE is a strong modulator of dopamine. Our innovation was a task in which an RPE event occurred precisely before onset of a movement. We probabilistically produced a combination of large or small, negative or positive RPE events before onset of a saccade, and observed that the vigor of the saccade that followed carried a robust signature of the preceding RPE event: high vigor saccades followed +RPE events, while low vigor saccades followed -RPE events. This suggests that control of vigor is partly through release of dopamine in the moments before onset of the movement.

neuroscience↗