Primary sensory cortices, top-down projections and conscious experience

Area of Science:

• Neuroscience
• Cognitive Neuroscience
• Sensory Perception

Background:

• A long-standing debate exists on whether neural activity in the primary visual cortex correlates with conscious visual experience.
• Studies using functional magnetic resonance imaging (fMRI) suggest a correlation, while single-neuron recordings indicate otherwise.
• Analogous questions in auditory and somatosensory systems have received less attention, yet show similar contradictory findings.

Purpose of the Study:

• To review studies on the role of primary auditory and somatosensory cortices in conscious experience.
• To reconcile contradictory findings regarding neural activity and conscious perception across sensory modalities.
• To propose a unifying hypothesis for conscious sensory processing.

Main Methods:

• Literature review of studies investigating neural activity in primary sensory cortices (visual, auditory, somatosensory).
• Analysis of findings from functional magnetic resonance imaging (fMRI) and single-neuron recordings.
• Synthesis of data to reconcile discrepancies and propose a theoretical framework.

Main Results:

• Studies in visual, auditory, and somatosensory systems present conflicting evidence on the correlation between primary cortical activity and conscious experience.
• Discrepancies in auditory and somatosensory systems mirror those found in the visual system.
• A proposed reconciliation suggests only top-down cortico-cortical signals in primary sensory cortices lead to conscious awareness.

Conclusions:

• Conscious perception is not a passive reflection of sensory input but an active interpretative process.
• Activity induced by top-down signals in primary sensory cortices is consciously accessible.
• Activity induced by bottom-up signals from the thalamus is not consciously accessible, offering a resolution to the debate.