Movement Control

Our studies of the primate frontal cortex focus on how decisions are made to respond or not to a moving object. Our initial single neuron work has targeted the supplementary eye field (SEF) which is a component of a complex of frontal brain regions associated with the the readiness, or bereitschafts, potential, a scalp-recorded electrical signal that occurs before movement that has been implicated in movement preparation and planning (1; 2). We have shown that this area is involved in generating anticipatory smooth pursuit (3; 4), smooth eye movements that precede target motion in order to reduce response time. Our recent studies focus on activity here that accompanyies the decision of whether or not to generate a pursuit movment to a moving object (5; 6). In these studies we use a paradigm we devised called ocular baseball that is adopted from the sport of baseball.

Adapted from Kim et al. JNP 2005

In the sport of baseball, a player swings a bat at a moving ball. A contingency on swinging the bat is that the ball cross a "strike zone," a small volume of space in front of the player. In ocular baseball, instead of swinging a bat, the observer makes a pursuit eye movement to follow a small target moving on a video screen. The strike zone is usually a square centered around a fixation spot. The observer fixates the spot while the target begins to move inward from the edge of the screen. If the moving spot enters the strike zone ("strike"), the player must pursue it. If the spot crosses the front edge of the strike zone without entering it ("ball"), the player must maintain gaze on the fixation point and inhibit the pursuit movement. Different populations of neurons in the SEF are active for strikes and balls (5). "Strike neurons" have early activity before the target crosses the plate on strike trials only. The early activity of "ball neurons" complements that of strike neurons and accompanies inhibition of the eye movements only on ball trials. Papers are in progress documenting that strike and ball neurons perform better than the observer in this task, and that they continue to signal the rule of ocular baseball even when the stimulus configuration is changed.

Strike neuron	Ball neuron

We have also conducted fMRI experiments on humans performing ocular baseball (6). In this work we found that addtionally the frontal eye files (FEF) and ventrolateral prefrontal cortex (VLPC) were activated when the visual properties of the stimulus and eye movements in the task were controlled for. This work motivated single-cell studies in the FEF and VLPFC that are part of our upcoming research plan.

Activation of frontal cortex during task (decided)
and no task (always) conditions

From Heinen et al., 2006 Journal of Neuroscience

The ocular baseball paradigm		Eye position and velocity in the task