Evidence for interhemispheric processing of inputs from the hands in human S2 and PV

Area of Science:

• Neuroscience
• Somatosensory System
• Human Brain Imaging

Background:

• The integration of sensory information from both hands is crucial for complex motor tasks.
• Understanding the neural mechanisms underlying bimanual somatosensory processing is essential for neuroscience.

Purpose of the Study:

• To identify cortical areas involved in integrating bimanual somatosensory inputs in the human brain.
• To compare brain responses to unilateral versus bilateral tactile stimulation.

Main Methods:

• Functional magnetic resonance imaging (fMRI) to assess brain activation extent.
• Magnetoencephalography (MEG) to determine the latency and characteristics of neural responses.

Main Results:

• fMRI showed significantly larger activation in the second somatosensory (S2) and parietal ventral (PV) areas for bilateral compared to unilateral stimulation.
• MEG revealed distinct temporal responses in the primary (S1) and secondary somatosensory cortices (S2/PV), with late responses (300-400 ms) in S2/PV during bilateral stimulation.
• S2/PV receives inputs from both contralateral and ipsilateral hands, with evidence of serial processing from S1 to S2.

Conclusions:

• The human somatosensory cortex, particularly S2/PV, plays a key role in integrating bimanual tactile information.
• Extensive intrahemispheric processing occurs in S2/PV before information is potentially transferred to the opposite hemisphere.
• Increased activation and delayed responses during bimanual stimulation may reflect increased neuronal activity, firing rate, or synchrony.