The raccoon lateral cervical nucleus: a single-unit analysis

Area of Science:

• Neuroscience
• Somatosensory System
• Tactile Perception

Background:

• The spinocervicothalamic system (SCTS) and dorsal column-medial lemniscal system (DC-MLS) are key pathways for processing tactile information.
• Understanding the properties of neurons in the lateral cervical nucleus (LCN), a component of the SCTS, is crucial for elucidating tactile processing.
• Previous studies have established characteristics of the raccoon SCT and DC-MLS, providing a basis for comparison.

Purpose of the Study:

• To characterize the receptive field properties and response characteristics of lateral cervical nucleus (LCN) neurons in raccoons.
• To compare the properties of LCN neurons with those of neurons in the spinocervical tract (SCT) and the dorsal column-medial lemniscal system (DC-MLS).
• To evaluate the contribution of the SCTS to the modality and place specificity of tactile information reaching the ventro-basal complex (VB) of the thalamus.

Main Methods:

• Electrophysiological recordings were performed on anesthetized raccoons.
• Neurons in the lateral cervical nucleus (LCN) were identified and characterized based on their responses to light tactile stimulation of peripheral body surfaces.
• Receptive field (RF) properties, including size and location, and response characteristics (rapidly adapting vs. slowly adapting, light touch vs. multireceptive) were analyzed.
• Neurons were antidromically activated from the contralateral thalamic ventro-basal complex (VB) or medial lemniscus to assess pathway involvement.

Main Results:

• A significant proportion of LCN neurons had receptive fields on the glabrous skin of the forepaw.
• Receptive fields on digits were smaller than those on the palm, and overall LCN receptive fields were larger than those in the SCT or DC-MLS.
• The proportion of rapidly adapting (RA) and slowly adapting (SA) neurons, as well as light touch versus multireceptive neurons, in the LCN was comparable to the SCT.
• Indentation velocity coding functions for both RA and SA units in the LCN showed homogeneous groupings, differing from the SCT and VB but similar to the DC-MLS.

Conclusions:

• The spinocervicothalamic system (SCTS), encompassing the LCN, generally lacks the high modality and place specificity observed in the DC-MLS.
• While the SCTS likely influences VB neuron properties, these properties are predominantly shaped by the more specialized DC-MLS.
• The findings suggest distinct roles for the SCTS and DC-MLS in tactile information processing, with the SCTS potentially contributing broader contextual information.