Corticofugal Modulation of Tactile Responses of Neurons in the Spinal Trigeminal Nucleus: A Wavelet Coherence Study

Corticofugal Modulation of Tactile Responses of Neurons in the Spinal Trigeminal Nucleus: A Wavelet Coherence Study

Eduardo Malmierca (Universidad Autónoma de Madrid, Spain), Nazareth P. Castellanos (Universidad Complutense de Madrid, Spain), Valeri A. Makarov (Universidad Complutense de Madrid, Spain) and Angel Nuñez (Universidad Autónoma de Madrid, Spain)
DOI: 10.4018/978-1-59904-996-0.ch001
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It is well know the temporal structure of spike discharges is crucial to elicit different types of neuronal plasticity. Also, precise and reproducible spike timing is one of the alternatives of the sensory stimulus encoding. This chapter studies a new mathematical analysis of the temporal structure of neuronal responses during tactile stimulation of the spinal trigeminal nucleus. We have applied the coherence analysis and the wavelet based approach for quantification of the functional stimulus - neural response coupling. We apply this mathematical tool to analyze the decrease of tactile responses of trigeminal neurons during the simultaneous application of a novel tactile stimulation outside of the neuronal receptive field (sensory-interference). These data suggest the existence of an attentional filter at this early stage of sensory processing.
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Somatosensory information coming from the face (including the mouth and the cornea) is collected, processed and finally sent to the thalamus by the trigeminal complex. For experimental study of the mechanism of information representation and processing the vibrissae sensory system of rodents is one of the most used models since it is particularly well organized and structured. Indeed, the large mystacial vibrissae of the rat are arranged in a characteristic, highly conserved array of five rows and up to seven arcs (Brecht et al., 1997; Welker, 1971). Rats use these facial whiskers to perform a variety of tactile discriminative tasks and behaviors (Carvell & Simons, 1990; Gustafson & Felbain-Keramidas, 1977). Sensory information from the vibrissae arrives to the trigeminal complex, which is organized in three sensory and one motor nuclei. The sensory trigeminal nuclei include: the principal nucleus (Pr5), the spinal nucleus (Sp5) and the mesencephalic nucleus (Me5). In turn Sp5 is divided into three subnuclei called oralis (Sp5O), interpolaris (Sp5I) and caudalis (Sp5C). In the trigeminal complex primary afferents and neurons form the “barrelettes”, which replicate the patterned arrangement of the whisker follicles on the snout (Ma, 1991).

Three classes of morphologically and physiologically distinguishable neurons reside in the rat trigeminal nucleus: barrelette cells, interbarrelette cells, and GABAergic or glycinergic inhibitory interneurons (Ressot et al., 2001; Viggiano et al., 2004).

The Pr5 and Sp5 trigeminal nuclei are obligatory synaptic relays for somatic sensory information originated in the large mystacial vibrissae or “whiskers’’ on one side of the face to the contralateral ventral posterior medial (VPm) nucleus of the thalamus (Peschanski, 1984; Smith, 1973). Pr5 projection neurons are characteristically described as having single-whisker receptive fields (RFs), whereas the rest of the population has RFs composed of multiple whiskers (Friedberg et al., 2004; Veinante & Deschênes 1999). In contrast, Sp5 thalamic neurons typically respond to more than four whiskers, and thus have larger RFs (Friedberg et al., 2004; Woolston et al., 1982). Thus, at the single-neuron level, there is a high degree of integration of tactile inputs from multiple whiskers in most trigeminal neurons.

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