A vestibulothalamic pathway: electrophysiological demonstration in the cat by localized cooling

A comparison of vestibular spatiotemporal tuning in macaque parietoinsular vestibular cortex, ventral intraparietal area, and medial superior temporal area

Vestibular responses have been reported in the parietoinsular vestibular cortex (PIVC), the ventral intraparietal area (VIP), and the dorsal medial superior temporal area (MSTd) of macaques. However, differences between areas remain largely unknown, and it is not clear whether there is a hierarchy in cortical vestibular processing. We examine the spatiotemporal characteristics of macaque vestibular responses to translational motion stimuli using both empirical and model-based analyses. Temporal dynamics of direction selectivity were similar across areas, although there was a gradual shift in the time of peak directional tuning, with responses in MSTd typically being delayed by 100-150 ms relative to responses in PIVC (VIP was intermediate). Responses as a function of both stimulus direction and time were fit with a spatiotemporal model consisting of separable spatial and temporal response profiles. Temporal responses were characterized by a Gaussian function of velocity, a weighted sum of velocity and acceleration, or a weighted sum of velocity, acceleration, and position. Velocity and acceleration components contributed most to response dynamics, with a gradual shift from acceleration dominance in PIVC to velocity dominance in MSTd. The position component contributed little to temporal responses overall, but was substantially larger in MSTd than PIVC or VIP. The overall temporal delay in model fits also increased substantially from PIVC to VIP to MSTd. This gradual transformation of temporal responses suggests a hierarchy in cortical vestibular processing, with PIVC being most proximal to the vestibular periphery and MSTd being most distal.

Spatial relationships between the terminations of somatic sensory motor pathways in the rostral brainstem of cats and monkeys. II. Cerebellar projections compared with those of the ascending somatic sensory pathways in lateral diencephalon

Previous studies have shown that ascending somatic sensory pathways arising from the dorsal column nuclei, lateral cervical nucleus and spinothalamic tract terminate in parts of the thalamus adjacent to those which receive cerebellar terminations. This termination pattern creates a border between the ventroposterolateral nucleus (VPL) and the ventrolateral nucleus (VL) in the cat and between the caudal and oral parts of VPL (VPLc and VPLo, respectively) in the monkey. Since it is not clear how sharp these borders are, a double orthograde labeling strategy was used in the present study to make direct comparisons of the projections to the thalamus from these sources of input. It was found that there was a change in the sources of afferent input to the different target areas that paralleled changes in cytoarchitecture. Moving caudally to rostrally, VPL in the cat and VPLc in the monkey received projections predominantly from the middle, dorsal (clusters) portion of the dorsal column nuclei. These projections were gradually replaced near the VPL-VL border in the cat and VPLc-VPLo border in the monkey first by input from the lateral cervical nucleus (cat only) and the rostral and ventral portions of the dorsal column nuclei and then by spinothalamic projections. Towards VL in the cat and the rostral parts of VPLo in the monkey (referred to as Vim by Hassler, '59 and Mehler, '71), these projections were in turn replaced by those from the cerebellum. This sequence resulted in a complex pattern (summarized in Fig. 10) where some thalamic territories received input predominantly from one source and others received converging input from several sources. The major region receiving converging ascending somatic sensory and cerebellar terminations was located at the border between VPL and VL in the cat and in the caudal parts of Olszewski's ('52) VPLo in the monkey (that is, between VPLc and Vim). In general, the results in the cat were similar to those in the monkey. One notable difference was that the domain containing terminals from the cerebellum and the rostral-ventral parts of the dorsal column nuclei was located medially between VPLc and Vim in the monkey, whereas it extended across the entire mediolateral border between VPL and VL in the cat. In both species, thalamic neurons received input predominantly from one afferent source and only minor input, if any, from other sources.(ABSTRACT TRUNCATED AT 400 WORDS)

The vestibulothalamic pathway: contribution of the ascending tract of Deiters

Axoplasmic transport techniques were used to determine the contribution of the ascending tract of Deiters (ATD) to the vestibulothalamic projection in cats. Large injections of HRP into the thalamus centered on the border region between the ventrobasal complex and the caudal ventrolateral nucleus resulted in bilateral retrograde labeling of cells in the vestibular nuclear complex and the nucleus prepositus hypoglossi (PH). Similar thalamic injections were also made in animals with extensive bilateral lesions of the medial longitudinal fasciculus (MLF) and the brachium conjunctivum (BC). HRP-positive neurons in these cases were localized principally to the ventral lateral vestibular nucleus and adjacent superior vestibular nucleus ipsilateral to the thalamic injection, evidence that vestibulothalamic neurons in these nuclei may project to the thalamus over the unlesioned ATD. Injections of [35S]methionine into the rostral vestibular nuclear complex in animals with MLF and BC lesions confirmed these findings, demonstrating orthograde transport of radiolabel in the ATD with termination in thalamus. These experiments document a contribution of the ATD to the ipsilateral vestibulothalamic projection; other sources of the vestibulothalamic pathway (PH, Y group) likely travel through projection systems destroyed in the lesions made in the present study.

Vestibular projections to the monkey thalamus: an autoradiographic study

Vestibulothalamic projections were studied in the monkey (macaca mulatta) by injecting anerograde trace substances (radioactive leucine and proline) into the vestibular nuclear complex. Terminal labelling was found bilaterally mainly in the nucleus ventroposterior lateralis pars oralis (VPLo) and to a lesser extent in the nucleus ventroposterior inferior (VPI) and nucleus ventralis lateralis pars caudalis (VLc). The labelling was sparse, and scattered over wide areas. The vestibular origin of this projection was confirmed by injecting retrograde tracer substances (horseradish peroxidase and 125I wheat germ agglutinin) into VPLo. In the autoradiographic study no labelling was found in the posterior group.

Afferent and efferent connections of the parabigeminal nucleus in cat revealed by retrograde axonal transport of horseradish peroxidase

Afferent and efferent connections of the parabigeminal nucleus (PBG) of the cat have been demonstrated by means of horseradish peroxidase (HRP) tracing technique. Following HRP injection in the PBG, labelled cells were observed mainly in the deep layers of the ipsilateral superior colliculus (SC). The other labelled structures were the prepositus hypoglossi complex (PH), the ventral nucleus of the lateral geniculate body (LGV), the locus coeruleus, the cuneiform nucleus, the periaqueductal gray and the dorsomedial hypothalamic area. Efferent projections of the PBG were investigated by HRP injection in SC, LGV, PH, hypothalamus and in some acoustic relays, i.e. medial geniculate body and inferior colliculus. Only the PBG-SC projection appeared to be well systematized. The positive labelling of the PBG following injection of LGV and hypothalamus is discussed in terms of the specificity of the injection. The absence of afferent and efferent connections of the PGB with any acoustic relay tends to exclude this nucleus from the auditory system in contrast to previous suggestions. On the basis of the close reciprocal PBG-SC connections a possible role of the PBG within visuomotor tectal function is proposed.