Investigating the mechanisms underlying saccade generation in the frontal eye fields using multisite microstimulation

Area of Science:

• Neuroscience
• Oculomotor Research
• Computational Neuroscience

Background:

• The frontal eye field (FEF) is crucial for controlling eye movements, with electrical microstimulation reliably evoking saccades.
• Understanding how microstimulation parameters influence saccades and how FEF population activity is decoded remains a challenge.

Purpose of the Study:

• To investigate the influence of microstimulation parameters on evoked saccades in the FEF.
• To compare different models for predicting saccade characteristics during dual-site FEF stimulation.
• To explore how the brain integrates FEF information for saccadic planning.

Main Methods:

• Used a 16-channel microelectrode array for microstimulation in the FEF of awake, behaving monkeys.
• Varied current intensities and stimulation sites (single vs. dual contacts).
• Developed and tested a polar average model against traditional vector sum and average models using FEF and superior colliculus (SC) data.

Main Results:

• Higher current intensities were needed to alter saccade direction compared to amplitude during single-site FEF stimulation.
• The polar average model outperformed traditional models in predicting both amplitude and direction of dual-site saccades.
• In the SC, the polar average model improved saccade amplitude prediction but not direction prediction.
• Model accuracy for unequal dual-site stimulation depended on individual site saccade amplitudes, suggesting flexible integration of FEF information.

Conclusions:

• Saccade direction and amplitude are differentially affected by FEF microstimulation intensity.
• A polar average model offers a more accurate framework for understanding FEF population activity readout for saccade generation.
• The brain appears to flexibly combine saccadic amplitude and direction information from the FEF for motor planning.