Intracortical arborizations and receptive fields of identified ventrobasal thalamocortical afferents to the primary somatic sensory cortex in the cat

Abstract

The intracortical arborizations of neurons from the ventroposterolateral thalamic nucleus (VPL) in the cat were studied by intraaxonal injections of horseradish peroxidase (HRP) following identification of their receptive fields. In the primary somatic sensory cortex (SI) VPL cells terminated in different cytoarchitectonic areas according to their receptive field modality. Fibers excited by deep tissue or joint rotation arborized preferentially in area 3a. Those responding tonically to cutaneous stimuli were located in the anterior part of area 3b; hairdriven cells terminated in area 3b and in the rostral pole of area 1. All fibers had a similar laminar distribution within SI. Axons terminated mostly in layers VI, iV, and the lower part of layer III. None terminated in layers I and II. Most terminal arbors were oriented along the mediolateral axis of the brain. The main arborization of a single VPL cell formed a bush of about 500 micrometers in diameter. some fibers generated two such bushes with an uninvaded region of about 300 micrometer between them. It is proposed that this patchy organization underlies in part the columnar organization of areas SI. Many VPL cells had secondary projection sites in SI. These were issued from smaller-sized collaterals and were located in a different cytoarchitectonic area than that of the main terminal plexuses. A significant number of these collaterals projected to area 4, Insufficient filling of the collaterals by HRP prevented a more complete characterization of the secondary arbors.

Mechanisms in Chronic Multisymptom Illnesses

“…These rods are anatomically defined by the terminal arbors of axons from the medial lemniscus (Hirai et al 1988; Rausell and Jones 1991) and are physiologically defined by neuronal responses to innocuous stimulation (Jones et al 1982; Kaas et al 1984; Lenz et al 1988b; Morrow and Casey 1992;Tremblay et al 1993). Thalamo-cortical fibers parallel the rod from which they originate (Landry and Deschenes 1981) and terminate in cortical columns (Jones et al 1982), consistent with the modality-specific organization in the primary sensory cortex (Jones et al 1982;Kaas 1983;Rausell et al 1992). Similarly, thalamic rods subserve different cutaneous structures (e.g., glabrous or hairy skin) consistent with the place-specific organization in the primary sensory cortex (Jones et al 1982 (Davis et al 1999;Ohara and Lenz 2003).…”

Auditory thalamocortical projections in the cat: Laminar and areal patterns of input

“…Three independent lines of evidence suggest that the profiles described here are a valid measure of thalamocortical input. First, axon-filling studies in visual cortex (Humphrey et al, 1985) and somatic sensory cortex (Landry and Deschênes, 1981) of physiologically identified afferents describe many features like those in the present study. They did not discern the class of giant axons as- Mesulam and Pandya (1973;monkey) Fink-Heimer, Nauta…”

Cortically-induced coherence of a thalamic-generated oscillation

“…22 Projections between thalamus and cortex were also topographic, but more divergent, consistent with anatomical studies. 29,33,40 The anatomical bases underlying this type of connectivity were detailed in previous papers. 19,22 In a previous study, 19 it was shown that calculating average membrane potentials using an intersite distance of 11 cells led to similar propagation velocity as in experiments, suggesting that this distance roughly corresponds to the interelectrode distance of 1 mm in the experimental setup.…”