Mapping quantal touch using 7 Tesla functional magnetic resonance imaging and single-unit intraneural...

Area of Science:

• Neuroscience
• Sensory Neuroscience
• Neuroimaging

Background:

• Understanding how the brain processes touch is crucial for developing advanced prosthetics and treating sensory disorders.
• Intraneural microstimulation (INMS) offers a way to directly activate specific nerve fibers, but its cortical representation is not fully understood.
• Ultra-high field 7 Tesla (7T) functional magnetic resonance imaging (fMRI) provides high spatial resolution for detailed brain mapping.

Purpose of the Study:

• To map the cortical and perceptual responses to INMS of single mechanoreceptive afferent units in the human median nerve.
• To compare brain activation patterns elicited by INMS with those from natural vibrotactile stimulation.
• To investigate the relationship between afferent input codes and their cortical representations.

Main Methods:

• Utilized ultra-high field 7T fMRI to image human brain activity.
• Performed INMS on single mechanoreceptive afferent units in the median nerve.
• Applied vibrotactile stimulation to the receptive field of the stimulated units.
• Analyzed brain activation maps and correlated them with perceptual reports.

Main Results:

• INMS and vibrotactile stimulation activated overlapping regions in the primary somatosensory cortex, corresponding to the specific digit representation.
• INMS also elicited activation in secondary somatosensory cortex, premotor cortex, primary motor cortex, insula, posterior parietal cortex, and contralateral prefrontal cortex.
• Perceptual reports aligned with the activated brain regions, indicating a link between INMS input and conscious perception.

Conclusions:

• The combination of INMS and 7T fMRI enables detailed mapping of human cortical responses to specific afferent inputs.
• This technique bridges the gap between the coding of first-order afferent input and its representation in the human cortex.
• Provides a powerful tool for understanding somatosensation and developing targeted neural interfaces.