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Modulation of neuronal activity in superior colliculus by changes in target probability
1Laboratory of Sensorimotor Research, National Eye Institute, Bethesda, Maryland 20892, USA.
Abstract:
Complex visual scenes require that a target for an impending saccadic eye movement be selected from a larger number of possible targets. We investigated whether changing the probability that a visual stimulus would be selected as the target for a saccade altered activity of monkey superior colliculus (SC) neurons in two experiments. First, we changed the number of possible targets on each trial. Second, we kept the visual display constant and presented a single saccade target repeatedly so that target probability was established over time. Buildup neurons in the SC, those with delay period activity, showed a consistent reduction in activity as the probability of the saccade decreased, independent of the visual stimulus configuration. Other SC neurons, fixation and burst, were largely unaffected by the changes in saccade target probability. Because we had monkeys making saccades to many locations within the visual field, we could examine activity associated with saccades outside of the movement field of neurons. We found the activity of buildup neurons to be similar across the SC, before the target was identified, and reduced when the number of possible targets increased. The results of our experiments are consistent with a role for this activity in establishing a motor set. We found, consistent with this interpretation, that the activity of these neurons was predictive of the latency of a saccadic eye movement and not other saccade parameters such as end point or peak velocity.
Insights
Altering saccade target probability affects superior colliculus (SC) buildup neuron activity. Reduced neuron activity correlates with decreased saccade probability, suggesting a role in motor set establishment.
Area of Science:
- Neuroscience
- Oculomotor Research
- Computational Neuroscience
Background:
- Selecting saccade targets in complex visual scenes involves processing multiple potential targets.
- The superior colliculus (SC) plays a crucial role in sensorimotor transformations, including eye movement control.
Purpose of the Study:
- To investigate how manipulating saccade target probability influences the activity of superior colliculus (SC) neurons.
- To determine if SC neuron activity changes based on the likelihood of a visual stimulus being selected as a saccade target.
Main Methods:
- Two experiments were conducted using monkeys performing saccadic eye movements.
- Experiment 1 varied the number of possible saccade targets per trial.
- Experiment 2 established target probability over time by repeatedly presenting a single target.
Main Results:
- Buildup neurons in the SC exhibited reduced activity as saccade probability decreased, irrespective of visual display configuration.
- Fixation and burst neurons in the SC were largely unaffected by changes in saccade target probability.
- Buildup neuron activity was reduced when the number of potential targets increased, suggesting a role in motor set formation.
Conclusions:
- SC buildup neuron activity is sensitive to saccade target probability, supporting its role in establishing a motor set.
- Buildup neuron activity predicts saccadic eye movement latency, not parameters like endpoint or peak velocity.
- These findings offer insights into the neural mechanisms underlying target selection and motor preparation in complex visual environments.
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