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PubMed1982

[Localization of neurons innervating vibrissae in the mouse in the Gasserian ganglion: retrograde peroxidase transport study and morphometric analysis].

Two methods were used in an attempt to localize within the trigeminal ganglion the neurons whose axons innervate mouse mystacial vibrissae. First, the loss in the bulk area occupied by neuronal cell bodies in the ophthalmo-maxillary part of the ganglion in two-month old mice, whose vibrissae follicles were coagulated unilaterally at birth, was evaluated morphometrically in four sectors of each section. Secondly, neurons labelled by the injection of peroxidase in the vibrissae follicles of adult mice were localized in the ganglion. The results indicate that the neurons which ensure the sensitive innervation of the vibrissae are situated in the median area of the ophthalmo-maxillary part of the ganglion, extending more rostrally than caudally, mainly in ventral position. A certain degree of somatotopy is demonstrated by the comparative study of neurons labelled by the injection of peroxidase in the anterior or posterior follicles. The neurons which correspond to the anterior vibrissae are mainly ventral, while they are both dorsal and ventral for the posterior vibrissae.

Animals↗
PubMed1988

Common fur and mystacial vibrissae parallel sensory pathways: 14 C 2-deoxyglucose and WGA-HRP studies in the rat.

Stimulation of mystacial vibrissae in rows A,B, and C increased (14C) 2-deoxyglucose (2DG) uptake in spinal trigeminal nucleus pars caudalis (Sp5c) mostly in ventral portions of laminae III-IV with less activation of II and V. Stimulation of common fur above the whiskers mainly activated lamina II, with less activation in deeper layers. The patterns of activation were compatible with an inverted head, onion skin Sp5c somatotopy. Wheatgerm Agglutinin-Horseradish Peroxidase (WGA-HRP) injections into common fur between mystacial vibrissae rows A-B and B-C led to anterograde transganglionic labeling only of Sp5c, mainly of lamina II with less label in layer V, and very sparse label in III and IV. WGA-HRP skin injections appear to primarily label small fibers, which along with larger fibers, were metabolically activated during common fur stimulation. Mystacial vibrissae stimulation increased 2DG uptake in ventral ipsilateral spinal trigeminal nuclei pars interpolaris (Sp5i) and oralis (Sp5o) and principal trigeminal sensory nucleus (Pr5). Common fur stimulation above the whiskers slightly increased 2DG uptake in ventral Sp5i, Sp5o, and possibly Pr5. The most dorsal aspect of the ventroposteromedial (VPM) nucleus of thalamus was activated contralateral to whisker stimulation. Stimulation of the common fur dorsal to the whiskers activated a region of dorsal VPM caudal to the VPM region activated during whisker stimulation. This is consistent with previous data showing that ventral whiskers and portions of the face are represented rostrally in VPM, and more dorsal whiskers and dorsal portions of the face are represented progressively more caudally in VPM. Mystacial vibrissae stimulation activated the contralateral primary sensory SI barrelfield cortex and a separate region in the second somatosensory SII cortex. Common fur stimulation above the whiskers activated a cortical region between the SI and SII whisker activated regions of cortex. It is proposed that this region represented the combined SI and SII common fur regions of somatosensory neocortex. Both whisker and common fur stimulation activated all layers of cortex, with layer IV being most activated followed by II-III, V, and VI. These data indicate that sensory input from the mystacial vibrissae in the adult rat is processed in brainstem, thalamic, and cortical pathways which are predominantly parallel to those which process information from the neighboring common fur sensory receptors.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1991

Central projections of primary sensory neurons innervating different parts of the vibrissae follicles and intervibrissal skin on the mystacial pad of the rat.

The cell bodies and central projections of neurons innervating the vibrissae follicles and adjacent skin in the rat were investigated by retrograde and transganglionic transport of HRP. The cell bodies of neurons innervating the vibrissa follicle via the deep vibrissa nerve (DVN) were the largest, followed by those innervating the follicle via the superficial vibrissa nerve (SVN). The smallest cell bodies were those innervating the intervibrissal skin. The DVN neurons terminated centrally as an almost uninterrupted column through the trigeminal sensory nuclear complex. The DVN projections to nucleus caudalis and C1 dorsal horn were entirely restricted to laminae III, IV, and V. Besides the projections to lamina V, the DVN projections were strictly localized somatotopically at all levels replicating the peripheral organization of the vibrissae. The SVNs projected sparsely to midlevels of the main sensory nucleus but not to nuclei oralis and interpolaris. The main SVN projections appeared in laminae I-III of nucleus caudalis. In addition, a small projection to lamina V was observed. The projections to laminae II and III were organized mediolaterally in a similar way as the DVN projections; those to laminae I and V were less restricted. The intervibrissal skin neurons projected sparsely to the caudal main sensory nucleus and to the border between nuclei oralis and interpolaris. The projections to nucleus caudalis were restricted to laminae I-III and V and were organized in a similar way as the SVN projections.

Afferent Pathways↗
PubMed1995

Patterning of local intracortical projections within the vibrissae representation of rat primary somatosensory cortex.

Anterograde and retrograde tracing with biotinylated dextran amine and Phaseolus vulgaris leukoagglutinin was used to assess projection patterns within the vibrissae representation of the rat's primary somatosensory cortex (S-I). Large and small injections of either tracer into the center of the vibrissae representation yielded dense anterograde and retrograde labelling throughout much of the tangential extent of the vibrissae representation within S-I. In all layers, the pattern and extent of retrograde and anterograde label was in rough congruence. The organization of this labelling varied across cortical layers. In layers II and III, labelled fibers extended away from injection sites in all directions and yielded a uniform pattern, which decreased in density with increasing distance from the tracer injection. There was a tendency for labelling to be more extensive along the representation of the row of vibrissae follicles that included the injection site than across rows. There was also a tendency for anterograde labelling to be more extensive in the direction of the representation of follicles more rostral on the face than that injected. In lamina IV, both labelled fibers and cells were restricted for the most part to the septa regions between the barrels. However, a small number of retrogradely labelled neurons were also located in the barrels (approximately one-ninth of the number found in the septa). The pattern observed in laminae II-III was repeated in layers V and VI. In these laminae, there was no evidence of a pattern of intracortical connections related to the vibrissae representation in overlying lamina IV.

Animals↗
PubMed1990

An examination of the intramodal and intermodal behavioral consequences of long-term vibrissae removal in rats.

An assessment was made of the effects of long-term tactile restriction by bilateral removal of the mystacial vibrissae from an early age on the subsequent somatosensory capacities of rats (i.e., the intramodal consequences) as well as its effects on visual and spatial capacities (i.e., the intermodal consequences). Rearing environment (enriched vs. normal) and method of vibrissae removal (cauterization of follicles vs. plucking) were examined to determine specific factors that m might influence the effect of vibrissae removal. Early, long-term tactile restriction had significant intramodal and intermodal consequences. Dewhiskered rats showed attenuated orientation to tactile stimuli presented to their mystacial pads and enriched-reared rats whose vibrissae follicles had been cauterized showed increased orientation to visual stimuli. Manipulation of early somatosensory signals had no impact on the development of certain spatial and precise manipulatory skills. These data provide limited evidence for theories of modality interdependence and yield basic information concerning the role of the mystacial vibrissae in the behavior of the rat.

Animals↗
PubMed1989

Asymmetries in crossed and uncrossed nigrostriatal projections dependent on duration of unilateral removal of vibrissae in rats.

The influence of unilateral removal of vibrissae on the crossed and uncrossed nigrostriatal projections was examined with the horseradish peroxidase tract tracing technique. Hemivibrissotomy mainly affected the projections arising from the rostral part of the substantia nigra. One to three days after clipping the vibrissae, rats were found to have more labeled neurons in the crossed projection to the caudate-putamen (CPU) on the same side as vibrissae removal than in the crossed projection to the CPU opposite to vibrissae removal. A reversed asymmetry was seen in rats examined 4-20 days after vibrissae removal. These animals had more labeled cells in the crossed and uncrossed projections terminating in the CPU opposite to the shaved side, i.e. in the hemisphere deprived of vibrissal sensory input. This time-course of neural alterations is similar to that of the recovery from behavioral asymmetries seen after hemivibrissotomy. Similar time-dependent alterations in the nigrostriatal projection had been found after unilateral injection of 6-OHDA into the substantia nigra.

Animals↗
PubMedDate not supplied

Reactions of neurons of the posterior ventral nucleus of the thalamus of the rat during movements of the vibrissae.

The reactions of neurons of the posterior ventral nucleus of the thalamus were investigated during movements of the vibrissae, accomplished independently by the animal, in experiments on rats utilizing a technique of partial curarization proposed by the author. Differences were identified in the pattern of the reactions of the thalamic neurons to deviation of a vibrissa by the experimenter from the pattern of the reactions of the same neurons to deviation of the vibrissa elicited by its hitting against a barrier during a sweep. A dependence of the response of the sensory neurons on whether or not the barrier was mobile during the period of the sweep of the vibrissae was also demonstrated. The hypothesis is advanced that at the thalamic level the analysis of the parameters of the stimulus is accomplished in connection with information regarding movements of the vibrissae.

Animals↗
PubMedDate not supplied

Blood flow dynamics in different layers of the somatosensory region of the cerebral cortex on the rat during mechanical stimulation of the vibrissae.

The present work reports studies of the quantitative spatial and temporal characteristics of changes in local blood flow in different layers of the somatosensory cortex of rats during adequate mechanical stimulation of the vibrissae. Studies were performed using 34 Wistar rats. Skull trepanning was performed under urethane (1 g/kg) anesthesia. Television-guided microscopy was used to introduce a set of three platinum electrodes (100 microns in diameter, with tip diameters of 30-40 microns) into the somatosensory cortex projection zone of the vibrissae. The first and third electrodes were positioned in cortical layers I-III and IV-VI and the central electrode was used to generate hydrogen within the tissue. Electrode positions were confirmed histologically after experiments. Animals were placed on artificial ventilation and one or all vibrissae were stimulated at a frequency of 3 Hz for 60 sec, with interstimulus intervals of 3 min. Changes in the local blood flow were measured during stimulation and for 1 min afterwards, using the hydrogen clearance method, and brain tissue impedance was also measured. There was a small (up to 5-7%) reduction in blood flow in the first seconds of stimulation, which was followed 15-25 sec later by an increase and subsequent return to initial when stimulation stopped. The increases in blood flow during stimulation of all vibrissae were by 24.2 +/- 6.7% (n = 36) in layers IV-VI and 24.5 +/- 5.6% (n = 34) in layers I-III; increases in response to stimulation of single vibrissae were by 19.4 +/- 7.4% (n = 28) and 17.8 +/- 6.4% (n = 28) respectively. The dynamics of impedance changes corresponded to those of blood flow changes. Thus, heterogeneity was found in changes of local brain blood flow in different layers of the somatosensory cortex during increases in cortical functional activity.

Animals↗
PubMed2005

Effects of vibrissae removal on search accuracy in the water maze.

In two experiments, the vibrissae were clipped on either the left, the right, or both sides, and the rats were trained to find a submerged platform in the Morris water maze. In both experiments, animals without vibrissae on both sides or on the left consistently spent significantly more time in the "counter" area twice the platform diameter in size, surrounding the submerged platform, than intact controls. Counter preference was not as consistent across experiments in rats with right vibrissae removed. These results suggest that the vibrissae are required for proprioceptive location of the platform itself, but not for proximal search accuracy. Since ischemic damage to hippocampal CA1 pyramidal cells has also been reported to prolong counter search during training, the results support the suggestion that impaired hippocampal processing of proprioceptive information from the vibrissae may contribute to the increased latency to find the platform shown by ischemic rats.

Analysis of Variance↗
PubMed1991

Vibrissa-related behavior in mice: transient effect of ablation of the barrel cortex.

Knowing that the mystacial vibrissae are an important part of the tactile sensory apparatus of rodents, we investigated the role of the barrel cortex - the endstation of the pathway between whiskerpad and cerebral cortex - in mouse behavior. We tested 15 female adult mice 2 and 10 weeks after both unilateral ablation of the barrel cortex and removal of the vibrissae on the same side in order to assess acute as well as transient effects of the cortical lesion. Two kinds of behavioral tests were performed on animals permanently provided with opaque lenses: one involved a passive stimulation of the vibrissae; the other was the 'gap-crossing' test which required the animal's active use of the vibrissae. Lesioned subjects did not show a deficit during passive stimulation of the vibrissae. On the contrary, there was a deficit during the gap-crossing test 2 weeks after the ablation of the barrel cortex. The deficit partly disappeared when the subjects were tested 10 weeks later. The results show that in mice, the barrel cortex is involved in the performance of complex behavioral tasks. The recovery of function could be due to changes in strategies to solve the gap-crossing test and/or to physical changes in neuronal circuitry. In either case, the results are relevant for the interpretation of cortical transplantation models using the whisker-to-barrel pathway.

Animals↗
PubMed1999

Early establishment of lesion-insensitive mature barrelettes corresponding to upper lip vibrissae in developing mice.

Vibrissae are tactile sense organs on the face of non-human mammals, and build up topographical representations in the brainstem trigeminal sensory nucleus called barrelettes. In the present study, we examined postnatal development of barrelettes corresponding to upper lip vibrissae by cytochrome oxidase (CO) histochemistry. At nuclear regions corresponding to upper lip vibrissae, a few segregated barrelettes first appeared at postnatal day 2 (P2), and segregation became clear for most upper lip barrelettes at P4. Compared with major barrelettes corresponding to mystacial vibrissae on the snout, the development of segregated pattern formation for upper lip barrelettes was retarded by 1-2 days. When vibrissa-related patterns were examined 5 days after infraorbital nerve transection, upper lip barrelettes became obscure in all mice lesioned at P1 and P2. Lesion-insensitive upper lip barrelettes first emerged in a few mice lesioned at P3 (33%), and the percentage attained 100% at P6. This temporal transition from lesion-sensitive to lesion-insensitive barrelettes was 3 days ahead of mystacial barrelettes. Therefore, upper lip barrelettes achieve rapid development within a narrow time frame during the first postnatal week. The early and rapid establishment of lesion-insensitive, mature barrelettes can be interpreted as suggesting the importance of oral sensory function in neonatal life.

Aging↗
PubMed2002

Effects of alterations of the vibrissae-related organization of thalamocortical axons upon the organization and outgrowth of intracortical connections in the barrelfield of the rat.

Previous studies have shown that intracortical projections in layer IV of the vibrissae representation of primary somatosensory cortex (S-I) are arrayed in a pattern complementary to that of thalamocortical axons (TCAs). Elevation of cortical serotonin (5-HT) in rats during the first postnatal week results in a transient disruption of the vibrissae-related pattern of TCAs and layer IV neurons in S-I. The present study examines the influence of elevated cortical 5-HT levels and the attendant loss of vibrissae-related TCA clusters on the organization of S-I intracortical connections. Cortical 5-HT was elevated in neonatal rats via chronic injections of clorgyline from birth until P-6. Animals were euthanized on P-6 or allowed to survive an additional 4 days without further clorgyline treatment. Distributions of TCAs and intracortical axons were assessed via application of 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate (Di-I) and 4-(4-(dihexadecylamino)styryl)-N-methylpyridinium iodide (Di-A) to the thalamic radiations and directly into the cortical barrelfield, respectively. Chronic administration of clorgyline resulted in a loss of the vibrissae-related organization of TCAs in layer IV of S-I. There was also a loss of the complementary pattern of intracortical projections in layer IV of this region. Discontinuation of clorgyline treatment resulted in a return of the vibrissae-related pattern of TCAs as well as the complementary pattern of intracortical projections. These results are consistent with the conclusion that the normal organization of intracortical projections in this region of S-I depends on the presence of the orderly array of TCAs.

Animals↗
PubMedDate not supplied

Selective breeding for variations in patterns of mystacial vibrissae of mice. Bilaterally symmetrical strains derived from ICR stock.

The establishment of certain patterns of mystacial vibrissae in mice has been the aim of an extensive breeding program carried on in this laboratory since 1977. In a companion paper we have reported on variations in this pattern in an outbred population of ICR mice. Starting with 21 ICR animals we bred, mostly by brother-sister mating, for 13 bilaterally symmetric patterns of mystacial vibrissae characterized by the presence (or absence) of supernumerary whiskers (SWs). The strains are classified as follows: I, a mouse strain with the standard pattern; II, eight strains bred for the occurrence of SWs at a given site or sites; and III, four mouse strains bred for a maximal number of SWs in different regions of the whiskerpad. Commonly, SWs occur in regions that coincide with the zones of mergence between the three facial processes except for two class II strains in which we bred for SWs in the "straddler" row of vibrissae, and for one class III strain, in which we cultivated the tendency (that appeared late in our program) to have SWs at the crest of a facial process. For classes I and II we analyzed the results for about 18 generations in terms of "improvement," meaning an increase in the percentages of animals with the desired phenotype together with a decreased frequency of undesired SWs. For class III, success in breeding meant the increase of the mean number of the desired SWs. All results led to the same conclusion: there is a genetic basis for the occurrence of SWs. The side preference of a particular SW is not strain dependent. It disappears in those class I and II strains in which almost 100% of animals obtained the desired phenotype. The increase in number of SWs in one zone of mergence does not depend on the presence of SWs in the other. Where tested, we almost always found a representation of an SW in a topologically equivalent location within the "barrelfield" area of the somatosensory cerebral cortex. Except for some diseases early in the breeding program, and some side effects of inbreeding that were eliminated, the population was without obvious defects. Where tested, there was no correlation between the occurrence of SWs and sex. The observed variations in pattern of mystacial vibrissae and their genetic background led us to propose a morphogenetic model for the formation of the pattern of mystacial vibrissae.

Animals↗
PubMed1994

Retinoic acid and mouse skin morphogenesis. I. Expression pattern of retinoic acid receptor genes during hair vibrissa follicle, plantar, and nasal gland development.

The spatial and temporal expression of the nuclear retinoic acid receptors alpha, beta, and gamma (RAR-alpha, beta, and gamma) was compared by in situ hybridization during hair vibrissa follicle and nasal and plantar eccrine gland morphogenesis in mouse embryo. The RAR-alpha and RAR-gamma transcripts are abundant in the dermal papilla cells of the hair vibrissa when these cells elicit epidermal hair placode (12.5-d embryos) and hair follicle (13.5-d embryos) formation. Both these transcripts are also abundant in the dermal cells of the plantar foot pad at the initiation stage (17.5-d embryos) of glandular morphogenesis. In epidermal cells, the distribution of RAR-gamma transcripts increases in parallel with hair vibrissa follicle and sweat gland differentiation, and thus may be part of the epidermal response to the dermal instructions. The RAR-beta signal is barely above control level during both hair vibrissa and plantar gland morphogenesis. By contrast, during nasal gland formation (12.5- to 15.5-d embryos), the RAR-beta signal reaches a high level in mesenchymal cells, whereas the RAR-alpha-transcripts are present in both epithelial and mesenchymal cells. These results suggest a role for RAR-alpha and RAR-gamma in the epidermal-dermal interactions that lead to hair follicle and plantar gland morphogenesis, whereas the nasal gland development implies RAR-alpha and RAR-beta gene expression. This should be correlated with the expression of the RAR-beta gene that was previously shown to be linked to the RA-induced glandular metaplasia of hair vibrissa follicles.

Animals↗
PubMed1996

Effect of neonatal axoplasmic transport attenuation in the infraorbital nerve on vibrissae-related patterns in the rat's brainstem, thalamus and cortex.

This study evaluated the effects of neonatal attenuation of axoplasmic transport in the infraorbital nerve (ION) on the organization of vibrissae-related patterns in the rat's CNS. Application of colchicine- or vinblastine- impregnated implants to the ION from birth until postnatal day (P)6 to P10 resulted in a 92.4% reduction in the number of trigeminal (V) ganglion cells labelled by application of horseradish peroxidase to the vibrissa pad and a 44.8% decrease in the number of Nissl-stained ganglion cells in the ophthalamic-maxillary portion of the V ganglion. These implants also decreased the number of myelinated fibres in the ION. In normal rats killed on P6-10, there was an average of 10273 +/- 1259 myelinated axons in the nerve. In the animals with colchicine- or vinblastine-treated implants, this value was 3891 +/- 1965. The highest axon count in an experimental animal was 9859. In all animals, axoplasmic transport attenuation resulted in the disappearance of normal vibrissae-related cytochrome oxidase patterns in the brainstem, thalamus and primary somatosensory cortex. Axoplasmic transport attenuation did not result in the disappearance of vibrissae-related ordering of V primary afferent terminal arbors, as demonstrated by anterograde labelling with neurobiotin. These results suggest that some factor conveyed from the periphery of the V ganglion and perhaps on to the brainstem is necessary for the maintenance of vibrissae-related patterns in the thalamus and cortex.

Afferent Pathways↗
PubMed1989

Efferent neurons and suspected interneurons in S-1 vibrissa cortex of the awake rabbit: receptive fields and axonal properties.

1. The behavioral tractability of the rabbit was exploited and enabled, in the fully awake state, receptive-field analysis of antidromically identified efferent neurons within the vibrissa representation of primary somatosensory cortex (S-1). Efferent neurons studied included ipsilateral corticocortical neurons (C-IC neurons, n = 56) that project to or beyond the second somatosensory cortical area (S-2) and corticofugal neurons of layer 5 (CF-5 neurons, n = 75) and layer 6 (CF-6 neurons, n = 92) that project to and/or beyond the thalamus. 2. An additional class of neurons was studied that was not activated antidromically from any stimulus site, but which responded synaptically to electrical stimulation of the ventrobasal (VB) thalamus with a burst of three or more spikes at frequencies of 600 to greater than 900 Hz. Most of these neurons also responded synaptically to stimulation of S-2. The action potentials of these neurons were much shorter (mean = 0.43 ms), than those of efferent neurons (mean = 0.98 ms). Such properties have been associated with interneurons found throughout the central nervous system, and these neurons are thereby referred to as suspected interneurons (SINs). Although SINs were found at all cortical depths, a strong peak in the distribution occurred just superficial to the peak in the distribution of CF-5 neurons. Most SINs located within this peak responded to deflection of only a single vibrissa. In contrast, SINs located in layer 6 and in layer 2-3 responded to deflection of many vibrissae (median = 11.0 and 5.5 vibrissae, respectively). In addition, SINs of layer 6 and layer 2-3 had significantly longer synaptic latencies to stimulation of VB thalamus than did SINs located at intermediate cortical depths. 3. The properties of efferent neurons and SINs differed considerably. Efferent neurons never responded to stimulation of VB thalamus with the high-frequency burst of spikes characteristic of SINs. Although greater than 70% of CF-6, CF-5 and C-IC neurons had receptive fields that were directionally selective, only 20% of SINs showed any degree of directional selectivity. Furthermore, SINs showed both much lower angular thresholds to vibrissa deflection and a much greater ability to follow high-stimulus frequencies than was seen in efferent neurons. The spontaneous firing rates of SINs had a mean value of 16.5 spikes/s, which was the highest seen in any population within S-1. 4. CF-5 neurons had a number of properties which contrasted with those of both CF-6 and C-IC neurons.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1983

Quantitative studies of stimulus coding in first-order vibrissa afferents of rats. 1. Receptive field properties and threshold distributions.

We examined stimulus-response relationships of vibrissa-activated mechanosensory neurons of the rat's fifth (trigeminal) ganglion. Single-unit activity was recorded with tungsten microelectrodes. The vibrissae were deflected with a variety of parametrically controlled stimulus waveforms. We found that the receptive field of each vibrissa-activated neuron consisted of a single vibrissa. Few, if any, unambiguous examples of spontaneous activity were observed in these neurons. Even if true spontaneous activity was present, its observed incidence was low, as were the measured discharge rates. Thresholds of individual neurons were usually quite discrete; often a 1-2% increase in pulse magnitude (angular displacement) above a level to which the neuron did not respond caused it to discharge on every trial. The distribution of thresholds for the sample was continuous with a median of about 1 degree and a range of over three orders of magnitude. The most sensitive neurons responded to deflections of less than 0.1 degrees. Many neurons responded to a single suprathreshold pulse with more than one spike. We found no consistent relationships among the thresholds of the additional evoked discharges of an individual neuron other than that the total number of evoked spikes either increased or stayed the same, but never decreased, as stimulus magnitude increased. About one-third of the neurons examined had velocity thresholds below 3 degrees/sec. Above that value, thresholds were distributed continuously throughout a range of over three orders of magnitude. The median velocity threshold was about 100 degrees/sec. The broad and continuous distributions of both magnitude and velocity thresholds suggest that a population of vibrissa-activated neurons can code stimulus strength smoothly and continuously over a wide range, even though individual neurons may be poorly suited to do so.

Animals↗
PubMed1983

Quantitative studies of stimulus coding in first-order vibrissa afferents of rats. 2. Adaptation and coding of stimulus parameters.

Mechanosensory neurons are often classified as either rapidly adapting or slowly adapting. We examined response decay (adaptation) during constant deflection of the vibrissae with quantitative, repeatable, ad hoc measures. We found that first-order vibrissa-activated neurons of the fifth ganglion exhibit a variety of adaptation rates that appear to be distributed continuously between the rapidly and slowly adapting extremes. Also, adaptation rate is influenced markedly by stimulus magnitude. We found no evidence for a dichotomy within the more slowly adapting neurons on the basis of discharge regularity. Threshold tuning curves were used to evaluate vibration sensitivity. Both the best frequencies and 1:1 discharge thresholds for sinusoidal stimulation ranged over two orders of magnitude and were continuously distributed. First-order vibrissa-activated afferents exhibit a broad variety of response patterns to constant-velocity stimulation. The pattern of discharge varied both as a function of time during constant-velocity (ramp) deflection and as a function of stimulus velocity. Although information about the parameters of a stimulus may be conveyed by any of several features of the response pattern, it appears that few if any neurons function as "pure" encoders of any particular stimulus parameter. We examined quantitatively the relationship between discharge rate and both velocity and amplitude of vibrissa deflection with the aid of a computer-based curve-fitting procedure. We found that about half the observed rate-level functions were best described by a power function; the remainder were best fit by a logarithmic function. The parameters of the best-fitting functions varied widely and continuously, emphasizing further the diversity of coding properties of the rat's vibrissa afferents. Rate-level curves for stimulus magnitude generally exhibited saturation; some were nonmonotonic. None were described adequately by either a logarithmic function or a power function.

Adaptation, Physiological↗