Tactile discrimination of textured surfaces: peripheral neural coding in the monkey

Area of Science:

• Neuroscience
• Sensory Physiology
• Computational Neuroscience

Background:

• Mechanoreceptive afferents in peripheral nerves are responsible for tactile sensation.
• Understanding how neural responses encode texture information is crucial for explaining tactile perception.

Purpose of the Study:

• To investigate how different types of mechanoreceptive afferents (rapidly adapting, slowly adapting, and pacinian) encode information about textured surfaces.
• To determine the role of these afferents in the psychophysical discrimination of texture properties.

Main Methods:

• Recordings from single mechanoreceptive afferents in monkey median and ulnar nerves.
• Stimulation of digital pads with textured surfaces of varying dot periods and lateral displacements.
• Analysis of neural response patterns, including temporal rhythm and mean response rates.

Main Results:

• Neural responses exhibited a temporal rhythm related to the texture's period and dependence on dot position and size.
• Rapidly adapting afferents showed increased response rates with larger dot periods (2.0 mm), suggesting a rate code.
• Pacinian afferents were more effective in transmitting information about period changes for smaller dot periods (1.0 mm).

Conclusions:

• Tactile discrimination of textured surfaces relies on information from a large population of afferents.
• A rate code, based on the mean number of impulses, is a plausible mechanism for encoding texture information, particularly for rapidly adapting and pacinian afferents under specific conditions.
• Different afferent populations contribute uniquely to the perception of texture based on its characteristics.