Single-unit activity in marmoset posterior parietal cortex in a gap saccade task

Area of Science:

• Systems Neuroscience
• Primate Models
• Oculomotor Control

Background:

• Abnormal saccadic eye movements are biomarkers for neuropsychiatric disorders.
• The common marmoset (Callithrix jacchus) is an emerging nonhuman primate model for studying saccadic control mechanisms.
• Previous work showed microstimulation in the marmoset posterior parietal cortex (PPC) elicits saccades.

Purpose of the Study:

• To record single-unit activity in the marmoset PPC during a saccadic task.
• To investigate the role of PPC neuronal activity in modulating saccadic reaction times, particularly the gap effect.
• To identify neuronal populations involved in saccadic preparation and target selection.

Main Methods:

• Single-unit activity was recorded from the PPC of two marmosets using chronic microelectrode arrays.
• Marmosets performed a saccadic task with interleaved gap and step trials.
• Neuronal responses were analyzed in relation to saccadic reaction times (SRTs) and trial type (gap vs. step).

Main Results:

• Marmosets exhibited a gap effect, with shorter SRTs in gap trials compared to step trials.
• Stronger neuronal responses during the gap period correlated with shorter SRTs, especially in "gap neurons".
• A significant proportion of "target neurons" showed responses related to saccadic targets, stronger in gap trials and correlating with SRTs.

Conclusions:

• The marmoset PPC plays a role in modulating saccadic preparation.
• Neuronal activity, including gap-related and target-related responses, influences saccadic timing.
• These findings support the marmoset as a valuable model for studying oculomotor control and related disorders.