Fixation cells in monkey superior colliculus. II. Reversible activation and deactivation

Area of Science:

• Neuroscience
• Oculomotor control
• Systems neuroscience

Background:

• The superior colliculus (SC) plays a crucial role in controlling eye movements.
• A specific neuronal population, termed fixation cells, in the rostral SC is hypothesized to regulate saccadic eye movements.

Purpose of the Study:

• To investigate the role of rostral SC fixation cells in the generation of saccadic eye movements.
• To test the hypothesis that these cells inhibit saccade generation.

Main Methods:

• Altering the activity of rostral SC fixation cells using electrical stimulation and GABAergic drugs (bicuculline and muscimol) in monkeys.
• Measuring saccade initiation latency and analyzing saccade characteristics.

Main Results:

• Electrical stimulation of fixation cells delayed saccade initiation and could interrupt ongoing saccades.
• Inhibiting GABAergic neurotransmission (bicuculline) increased saccade latency.
• Enhancing GABAergic inhibition (muscimol) reduced saccade latency and led to increased express saccades, suggesting a role in suppressing them.

Conclusions:

• Fixation cells in the rostral SC actively inhibit saccadic eye movement generation.
• These cells are integral to the oculomotor system controlling visual fixation and modulating saccade frequency, including express saccades.