Thalamus exhibits less sensory variability quenching than cortex

Area of Science:

• Neuroscience
• Computational Neuroscience
• Systems Neuroscience

Background:

• Neuronal spiking variability is a key characteristic of brain activity.
• Stimulus onset significantly reduces trial-to-trial variability in cortical areas.
• The response dynamics of the thalamus, particularly the pulvinar, remain largely uncharacterized regarding variability.

Purpose of the Study:

• To investigate trial-to-trial spiking variability in the pulvinar and lateral geniculate nucleus (LGN) compared to visual cortex (area V4).
• To determine if visual stimulus onset affects variability in these thalamic nuclei similarly to the cortex.
• To explore potential differences in variability quenching mechanisms between thalamus and cortex.

Main Methods:

• Electrophysiological recordings from two adult rhesus macaques during a perceptual task.
• Comparative analysis of neuronal spiking variability in the ventral and dorsal pulvinar, LGN, and area V4.
• Assessment of variability changes before and after visual stimulus presentation.

Main Results:

• Baseline spiking variability was lower in the pulvinar and LGN than in area V4.
• Visual stimulus onset markedly reduced variability in area V4 but had minimal effect on thalamic nuclei.
• A small, significant variability decrease was observed in the dorsal pulvinar, but not the ventral pulvinar.
• These differences were independent of response strength or mean firing rates.

Conclusions:

• The thalamus exhibits distinct trial-to-trial variability dynamics compared to the visual cortex.
• Visual stimulation does not quench variability in the pulvinar and LGN as effectively as in V4.
• Dissociated variability reduction in pulvinar subregions suggests specialized functional roles and differing mechanisms of neural processing.