Tactile Environment Research Articles

Cortex-restricted deletion of Foxp1 impairs barrel formation and induces aberrant tactile responses in a mouse model of autism

BackgroundMany children and young people with autism spectrum disorder (ASD) display touch defensiveness or avoidance (hypersensitivity), or engage in sensory seeking by touching people or objects (hyposensitivity). Abnormal sensory responses have also been noticed in mice lacking ASD-associated genes. Tactile sensory information is normally processed by the somatosensory system that travels along the thalamus to the primary somatosensory cortex. The neurobiology behind tactile sensory abnormalities, however, is not fully understood.MethodsWe employed cortex-specific Foxp1 knockout (Foxp1-cKO) mice as a model of autism in this study. Tactile sensory deficits were measured by the adhesive removal test. The mice’s behavior and neural activity were further evaluated by the whisker nuisance test and c-Fos immunofluorescence, respectively. We also studied the dendritic spines and barrel formation in the primary somatosensory cortex by Golgi staining and immunofluorescence.ResultsFoxp1-cKO mice had a deferred response to the tactile environment. However, the mice exhibited avoidance behavior and hyper-reaction following repeated whisker stimulation, similar to a fight-or-flight response. In contrast to the wild-type, c-Fos was activated in the basolateral amygdala but not in layer IV of the primary somatosensory cortex of the cKO mice. Moreover, Foxp1 deficiency in cortical neurons altered the dendrite development, reduced the number of dendritic spines, and disrupted barrel formation in the somatosensory cortex, suggesting impaired somatosensory processing may underlie the aberrant tactile responses.LimitationsIt is still unclear how the defective thalamocortical connection gives rise to the hyper-reactive response. Future experiments with electrophysiological recording are needed to analyze the role of thalamo-cortical-amygdala circuits in the disinhibiting amygdala and enhanced fearful responses in the mouse model of autism.ConclusionsFoxp1-cKO mice have tactile sensory deficits while exhibit hyper-reactivity, which may represent fearful and emotional responses controlled by the amygdala. This study presents anatomical evidence for reduced thalamocortical connectivity in a genetic mouse model of ASD and demonstrates that the cerebral cortex can be the origin of atypical sensory behaviors.

FOLL-E: Teaching First Order Logic to Children

First-order logic (FO) is an important foundation of many domains, including computer science and artificial intelligence. In recent efforts to teach basic CS and AI concepts to children, FO has so far remained absent. In this paper, we examine whether it is possible to design a learning environment that both motivates and enables children to learn the basics of FO. The key components of the learning environment are a syntax-free blocks-based notation for FO, graphics-based puzzles to solve, and a tactile environment which uses computer vision to allow the children to work with wooden blocks. The resulting FOLL-E system is intended to sharpen childrens' reasoning skills, encourage critical thinking and make them aware of the ambiguities of natural language. During preliminary testing with children, they reported that they found the notation intuitive and inviting, and that they enjoyed interacting with the application.

The People of Hamtramck: Some Reflections on Belonging, Agency, and Being Polish American

Abstract This article presents a selective portrayal of the Polish Americans of Hamtramck based on a collection of oral interviews conducted in the summers of 2014 and 2015. It argues that Hamtramck is best understood through the concept of “tangible belonging,” which historian John Swanson defines as an identity that is built in connection with a mental construct derived from the tactile environment in which an individual lives and experiences through the various senses of vision, sound, smell, touch, and so forth. Each generation and wave of immigrants understood differently their Polish and Polish American identity, which developed via a complex connection with Hamtramck's fabric of life over the years.

An artificial piezotronic synapse for tactile perception

Intelligent neuromorphic tactile perception architecture requires the integration of pressure sensors, connecting cables, and artificial synapses, which poses serious challenges to complex device integration and overall energy consumption. Therefore, the development of self-adaptive, high performance and sophisticated artificial synapses with an uncomplicated fabrication process that can adjust its output with the tactile environment is essential. Here, we developed a proof-of-concept simple two-terminal, highly transparent, and flexible piezotronic artificial synapse that emulates environment-adaptable tactile perception. Specifically, all typical synaptic functions, such as excitation/depression, plasticity, and paired-pulse facilitation, are sensitive to the applied strain, thus providing artificial in-situ “touch sensing”. The observed effect is attributed to the dynamic charge trapping/detraining via strain-modulated band alignment and is qualitatively confirmed by Kelvin probe force microscopy measurements. The presented work provides new insights into simplifying the circuitry of neuromorphic tactile perception, resulting in a number of additional applications toward skin‐attachable electronics, robotics, and prosthetics. A highly transparent, flexible, and piezotronic two-terminal artificial synapse has been developed that emulates environment-adaptable tactile perception. All typical synaptic functions, such as excitation/depression, plasticity, and paired-pulse facilitation, are sensitive to the applied strain, thus providing artificial in-situ “touch sensing”. Presented work provides new insights into simplifying the circuitry of neuromorphic tactile perception toward skin‐attachable electronics, robotics, and prosthetics applications.

Specialized mechanoreceptor systems in rodent glabrous skin.

Key points An ex vivo preparation was developed to record from single sensory fibres innervating the glabrous skin of the mouse forepaw.The density of mechanoreceptor innervation of the forepaw glabrous skin was found to be three times higher than that of hindpaw glabrous skin.Rapidly adapting mechanoreceptors that innervate Meissner's corpuscles were severalfold more responsive to slowly moving stimuli in the forepaw compared to those innervating hindpaw skin.We found a distinct group of small hairs in the centre of the mouse hindpaw glabrous skin that were exclusively innervated by directionally sensitive D‐hair receptors.The directional sensitivity, but not the end‐organ anatomy, were the opposite to D‐hair receptors in the hairy skin.Glabrous skin hairs in the hindpaw are not ubiquitous in rodents, but occur in African and North American species that diverged more than 65 million years ago. Rodents use their forepaws to actively interact with their tactile environment. Studies on the physiology and anatomy of glabrous skin that makes up the majority of the forepaw are almost non‐existent in the mouse. Here we developed a preparation to record from single sensory fibres of the forepaw and compared anatomical and physiological receptor properties to those of the hindpaw glabrous and hairy skin. We found that the mouse forepaw skin is equipped with a very high density of mechanoreceptors; >3 times more than hindpaw glabrous skin. In addition, rapidly adapting mechanoreceptors that innervate Meissner's corpuscles of the forepaw were severalfold more sensitive to slowly moving mechanical stimuli compared to their counterparts in the hindpaw glabrous skin. All other mechanoreceptor types as well as myelinated nociceptors had physiological properties that were invariant regardless of which skin area they occupied. We discovered a novel D‐hair receptor innervating a small group of hairs in the middle of the hindpaw glabrous skin in mice. These glabrous skin D‐hair receptors were direction sensitive albeit with an orientation sensitivity opposite to that described for hairy skin D‐hair receptors. Glabrous skin hairs do not occur in all rodents, but are present in North American and African rodent species that diverged more than 65 million years ago. The function of these specialized hairs is unknown, but they are nevertheless evolutionarily very ancient. Our study reveals novel physiological specializations of mechanoreceptors in the glabrous skin that likely evolved to facilitate tactile exploration.

Sensitivity to auditory-tactile colocation in early infancy.

An ability to detect the common location of multisensory stimulation is essential for us to perceive a coherent environment, to represent the interface between the body and the external world, and to act on sensory information. Regarding the tactile environment "at hand", we need to represent somatosensory stimuli impinging on the skin surface in the same spatial reference frame as distal stimuli, such as those transduced by vision and audition. Across two experiments we investigated whether 6- (n = 14; Experiment 1) and 4-month-old (n = 14; Experiment 2) infants were sensitive to the colocation of tactile and auditory signals delivered to the hands. We recorded infants' visual preferences for spatially congruent and incongruent auditory-tactile events delivered to their hands. At 6 months, infants looked longer toward incongruent stimuli, whilst at 4 months infants looked longer toward congruent stimuli. Thus, even from 4 months of age, infants are sensitive to the colocation of simultaneously presented auditory and tactile stimuli. We conclude that 4- and 6-month-old infants can represent auditory and tactile stimuli in a common spatial frame of reference. We explain the age-wise shift in infants' preferences from congruent to incongruent in terms of an increased preference for novel crossmodal spatial relations based on the accumulation of experience. A comparison of looking preferences across the congruent and incongruent conditions with a unisensory control condition indicates that the ability to perceive auditory-tactile colocation is based on a crossmodal rather than a supramodal spatial code by 6 months of age at least.

Computational modeling indicates that surface pressure can be reliably conveyed to tactile receptors even amidst changes in skin mechanics.

Distinct patterns in neuronal firing are observed between classes of cutaneous afferents. Such differences may be attributed to end-organ morphology, distinct ion-channel complements, and skin microstructure, among other factors. Even for just the slowly adapting type I afferent, the skin's mechanics for a particular specimen might impact the afferent's firing properties, especially given the thickness and elasticity of skin can change dramatically over just days. Here, we show computationally that the skin can reliably convey indentation magnitude, rate, and spatial geometry to the locations of tactile receptors even amid changes in skin's structure. Using finite element analysis and neural dynamics models, we considered the skin properties of six mice that span a representative cohort. Modeling the propagation of the surface stimulus to the interior of the skin demonstrated that there can be large variance in stresses and strains near the locations of tactile receptors, which can lead to large variance in static firing rate. However, variance is significantly reduced when the stimulus tip is controlled by surface pressure and compressive stress is measured near the end organs. This particular transformation affords the least variability in predicted firing rates compared with others derived from displacement, force, strain energy density, or compressive strain. Amid changing skin mechanics, stimulus control by surface pressure may be more naturalistic and optimal and underlie how animals actively explore the tactile environment.

The rewarding properties of methamphetamine in an invertebrate model of drug addiction

The rewarding properties of drugs in the mammalian system depend on their ability to activate appetitive motivational states. The associated underlying mechanism is strongly conserved in evolution and invertebrates have recently emerged as a powerful new model in addiction research. The natural reward system in crayfish has surprisingly proven sensitive to human drugs of abuse, providing a new model for research into the basic biological mechanisms of drug addiction. In this study, we examined the presence of natural reward systems in crayfish, and then characterized its sensitivity to 2.5μg/g, 5.0μg/g and 10.0μg/g doses of methamphetamine (METH). Using the conditioned place preference (CPP) paradigm, we demonstrated that irrespective of the number of doses of METH injected into the pericardial system, crayfish seek out a particular tactile environment that had previously been paired with the METH. This study demonstrates that crayfish offer a comparative and complementary approach in addiction research. It contributes an evolutionary context to our understanding of a key component in learning and of natural reward as an important life-sustaining process.

Tactile modulation of hippocampal place fields

Neural correlates of spatial representation can be found in the activity of the hippocampal place cells. These neurons are characterized by firing whenever the animal is located in a particular area of the space, the place field. Place fields are modulated by sensory cues, such as visual, auditory, or olfactory cues, being the influence of visual inputs the most thoroughly studied. Tactile information gathered by the whiskers has a prominent representation in the rat cerebral cortex. However, the influence of whisker-detected tactile cues on place fields remains an open question. Here we studied place fields in an enriched tactile environment where the remaining sensory cues were occluded. First, place cells were recorded before and after blockade of tactile transmission by means of lidocaine applied on the whisker pad. Following tactile deprivation, the majority of place cells decreased their firing rate and their place fields expanded. We next rotated the tactile cues and 90% of place fields rotated with them. Our results demonstrate that tactile information is integrated into place cells at least in a tactile-enriched arena and when other sensory cues are not available.

The Deepest Sense: A Cultural History of Touch by Constance Classen

Reviewed by: The Deepest Sense: A Cultural History of Touch by Constance Classen Sara Spike Classen, Constance – The Deepest Sense: A Cultural History of Touch. Chicago: University of Illinois Press, 2012. Pp. 227. In The Deepest Sense: A Cultural History of Touch, Constance Classen gives readers a “feel” for medieval and early modern Europe while demonstrating the centrality of touch to the social, cultural, and religious formations of premodernity. More broadly, she advocates for sensory history, and for the role that scholars in the social sciences and humanities have to play in our understanding of the senses. Early in the book Classen reminds readers that “to rely on science for a true understanding of perception is both to disregard the ways in which science is itself a social construct and to detract from the significance of culturally specific models of sensation” (p. xv). The sensory practices and symbolism of any period and its cultural values and norms are closely related and indeed mutually constituted. Foregrounding the senses therefore provides an innovative analytical lens for understanding past cultures; Classen argues that such analyses have the potential to make the “dry bones of historical fact…more interesting and more memorable” (p. xii). Classen defines touch broadly to include not just bodily contact, but also the sensations associated with temperature, corporeal movement, pleasure, pain and other aspects of embodied experience. She also carefully acknowledges the multisensory nature of human experience rather than trying to disentangle touch from the other senses. Drawing such wide boundaries around her subject allows Classen to investigate an eclectic range of ideas and experiences related to touch by exploring “the tactile values that shaped the sensibility and sociality” of medieval and early modern Europe (p. xiii). The Deepest Sense challenges the common assertion that the transition to modernity can be charted through a straightforward narrative of the rise of the cultural importance of vision – which Enlightenment thinkers came to associate with rationalism – and a corresponding decline in the primacy of touch – which the same thinkers associated with primitivism and base emotion. This is, of course, an embodied version of the equation that allowed the Middle Ages to be characterized and dismissed as “dark.” Classen problematizes these assumptions, arguing that “the sensory patterns of history are too complex” for such a simplified account (p. 159). She writes that “touch does not simply recede from cultural life in modernity, it is re-educated, and while it retreats from some domains, it expands into others” (p. xiv). For example, although Classen would not suggest that one replaced the other, the practice of touching artifacts was newly banished from museums and art galleries in the nineteenth century at the same time that the rise of the department store (regularly cited as representative of the new regime of vision) provided a new public venue for handling both precious and profane objects. This shift, [End Page 229] and the persistence of touch in modernity, which Classen uses “in the sociological sense to refer to the period beginning with the eighteenth century” (p. xiii), are detailed in the final two chapters of the book. The majority of the text focuses on the tactile realms of medieval and early modern Europe, providing a compelling account of a fundamentally “hands-on” culture. Following a short preface, Classen draws the reader into a world of communal living, sleeping, eating, and bathing, where bodies regularly came into contact. The warmth of the hearth, the feel of a soft or hard bed, the physical strains of feudal agriculture, the weighty armour and painful blows of knighthood, and the pleasures of games and fairs are among the sensations that characterized a tactile environment both seemingly familiar and very foreign to our own. The extent to which religion underwrote sensory values is also made clear. Unlike the prioritization of iconography and the written word in later periods, Classen makes the case that touch was the predominant sense of early Christian piety. This is exemplified by the theological interest in the tangible corporeality of Christ, embodied rites of physical penance, the numerous cults of relics for which physical contact was profoundly meaningful, the relationship between bodily suffering and the torments of Hell, and the...

Reversing the {Im}material Sense of a Nonplace

This article explores the Brussels metro as a nonplace and considers the impact of blindness on nonplace. In discussing the {im}materiality of the metro, this article focuses on the experience of metro-time as “waiting and anticipation” and metro-space as “alone-together.” Along with this, the notion of a dialogue with blindness is introduced into this nonplace. We explore the relation between metro and blindness as dialogue: the meeting and aversion of two actors in the particular context of the Brussels metro. In this, the authors identify how the investment of particular agents makes the metro space more malleable. Two strategies are used, one considers the different world in which blind people live and experience spatial environments, thus suggesting the invasion of “another world” into a nonplace. The second strategy considers embodiment and performance, and how contextual features afford new representations and pathways through and into a nonplace. At the core of this work is an argument that illustrates how the dialogue between blindness and public space can reverse the quality of the {im}material sense of a nonplace. The ethnographic work that serves as the background for this article is twofold. First, observation of daily travel on the metro brings an understanding of the general characteristics of the metro system, which includes human interaction/s and performance. Second, through observation and documentation of a group of disability advocates, educators, designers, and planners worked together to create a more accessible metro system for people who are blind and visually impaired. Finally, it is argued that fundamentally, a dialogue with disability reverses the {im}material sense of a nonplace. The potential of blindness in reversing the metro’s nonplace qualities stems from the articulation of a sensory vulnerability in a time where vision has achieved a dominant position. Blindness-as-vulnerability is a significant agent for intra-action in the Brussels metro system, making it a safer environment, a more tactile environment, and one where information is added for the benefit of a particular group and also extending to all people.

Adam Smith and the Problem of the External World

How does the mind attribute external causes to internal sensory experiences? Adam Smith addresses this question in his little known essay ‘Of the External Senses.’ I closely examine Smith's various formulations of this problem and then argue for an interpretation of his solution: that inborn perceptual mechanisms automatically generate external attributions of internal experiences. I conclude by speculating that these mechanisms are best understood to operate by simulating tactile environments.

Glowing Pathfinder Bugs: A Natural Haptic 3D Interface for Interacting Intuitively with Virtual Environments

Glowing Pathfinder Bugs is an interactive art project primarily aimed at children and created by the digital arts group Squidsoup. It uses projection to visualize virtual bugs on a real sandpit. The bugs are aware of their surroundings and respond to its form in their vicinity. By altering the topography of the sand, participants affect the bugs' environment in real time, facilitating direct communication between them and computer-generated creatures. This highly malleable and tactile physical environment lets us define and carve out the landscape in which the creatures exist in real time. Thus, virtual creatures and real people coexist and communicate through a shared tactile environment. Participants can use natural modes of play, kinesthetic intelligence, and their sense of tactility to collaboratively interact with creatures inhabiting a hybrid parallel world. This paper describes the project and analyzes how children in particular respond to the experience; it looks at the types of physical formations that tend to be built and notes how children instinctively anthropomorphize the bugs, treating projected imagery as living creatures — though with a ludic twist.

A Shape Display Method Based on Electromagnetic Localization and Actuation

A 3D shape display method based on electromagnetic localization and actuation is presented and the correspondent miniature device is developed. Evaluation of the single actuator device shows that majority of shape information can be delivered. The device containing multiple actuators is designed to improve the small shape and large curvature perception. The scaling analysis of EM force is performed to determine the maximal allowable actuators per unit area. The prototype device containing 4 £ 4 actuators array is developed for further evaluation. The need to display graphics to visually impaired people has been growing with the emergence of World Wide Web (WWW). Although several types of computer-aided software were devised to transfer selective information into Braille language, the major obstacle of the communication for the visually impaired people is the deflcient delivery of the graphic information. As a reason, the interest has arisen in developing shape display devices. Electronic devices aiming to fulflll this function can be categorized into two groups. One is to use active touch method where the proflle of the shape is produced by using a tactile matrix (1,2) or virtual environment through force feedback (3). These devices, however, either demand a relatively large platform to incorporate a touching interface, or require large driving element to produce enough force to users. The other group of devices is to use passive sensing method where the pattern is locally produced onto human skin by using spatially discriminated stimulation (4), which is mainly successful for two dimensional graphs. This paper presents an approach that combines both active and passive tactile method to dis- play three dimensional virtual objects by using the miniature vibrator(s). The presented device incorporates an electromagnetic (EM) position detector and EM actuator(s) to selectively stimu- late user's flnger based on its location. The working principle is shown by the block diagram in Figure 1. Human brain interacts with the EM actuator as receiving stimulation and guides the flnger to move following user's estimate of the reference shape. The position comparison results in a decision to engage the actuator in selective locations. The iterations of receiving stimulation and modifying shape estimates produce to users an optimal estimation of the shape.

Drug-seeking behavior in an invertebrate system: Evidence of morphine-induced reward, extinction and reinstatement in crayfish

Several lines of evidence suggest that exploring the neurochemical basis of reward in invertebrate species may provide clues for the fundamental behavioral and neurobiology underpinnings of drug addiction. How the presence of drug-sensitive reward relates to a decrease in drug-seeking behavior and reinstatement of drug-seeking behavior in invertebrate systems is not known. The present study of a conditioned place preference (CPP) paradigm in crayfish (Orconectes rusticus) explores morphine-induced reward, extinction and reinstatement. Repeated intra-circulatory infusions of 2.5 μg/g, 5.0 μg/g and 10.0 μg/g doses of morphine over 5 days serve as a reward when paired with a distinct visual or tactile environment. Morphine-induced CPP was extinguished after repeated saline injections for 5 days in the previously morphine-paired compartment. After the previously established CPP had been eliminated during the extinction phase, morphine-experienced crayfish were challenged with 2.5 μg/g, 5.0 μg/g and 10.0 μg/g, respectively. The priming injections of morphine reinstated CPP in all training doses, suggesting that morphine-induced CPP is unrelenting, and that with time, it can be reinstated by morphine following extinction in an invertebrate model just like in mammals. Together with other recent studies, this work demonstrates the advantage of using crayfish as an invertebrate animal model to investigate the basic biological processes that underline exposure to mammalian drugs of abuse.

Identification and characterization of somatosensory off responses

Event-related potentials (ERPs) have been recorded in response to the offset of sensory stimulation in both the auditory and visual modalities. The present experiment employed vibratory stimulation to characterize somatosensory ERPs in response to different duration stimuli. In two separate experiments, we recorded attended and unattended somatosensory ERPs to 70 Hz, sine wave stimuli using the following durations: 20 ms, 50 ms, 70 ms, 150 ms, 170 ms, 250 ms and 1000 ms. An oscillating coil delivered stimuli through a ‘T-bar’ to digits 2 and 3 of the right hand. The amplitude and latency measurements of P50, P100 and a later negative component (No1) were analyzed using MANOVA. There was no significant difference in the latency values of the P50 and P100, but as the duration increased, there was a significant increase ( P < 0.01) in the latency of No1. No1 appeared 130 ms ± 9 ms following the offset of the stimulus. Amplitude values of the P50 and P100 components decreased as the stimulus duration increased and this effect became significant ( P < 0.05) as the duration difference increased. Stimuli of 150 ms or greater evoked a negative baseline shift that persisted for the duration of the stimulus and area measurements in 7 out of the 10 subjects showed a significant increase in amplitude when the stimulus was attended. An intracranial case study supported these findings. The characteristics of the No1 component indicate it is a somatosensory off response, and it, in conjunction with the P50 and sustained potential, may reflect activity of a neural system that is responsive to changes in the tactile environment.

Comparison of blind and sighted participants' performance in a letter recognition working memory task

The performance in letter recognition of 21 blind participants was compared with that of 16 age-matched sighted participants in an n-back working memory task. Blind participants were tested tactually with series of raised letters and Braille characters, and sighted participants tactually with series of raised letters and visually with series of letters presented on a computer screen. With this approach, we wanted to compare the tactual performances by trained (blind) and non-trained (sighted) participants, and tactual and visual performances by trained (blind and sighted, respectively) participants. Increments of mnemonic load increased the number of incorrect responses significantly in all n-back tasks. As expected, the blind participants outperformed the sighted ones statistically significantly in the tactile raised letters n-back task. The sighted participants produced significantly fewer incorrect responses in the visual task than the blind participants in the raised letters task, whereas there was no such difference between sighted subjects' visual performance and blind subjects' tactile performance in the Braille task. These results demonstrate the degree and limits to which everyday practice develops perceptual skills either in persons without sensory deficits (vision and visual environment), or persons with severe sensory loss (blindness and tactile environment). The performance level of blind persons relying on their tactile skills is just about the same as that of sighted subjects relying on their visual skills.

Temporal shaping of phasic neuronal responses by GABA- and non-GABA-mediated mechanisms in the somatosensory thalamus of the rat

Trapezoidal mechanical movement of whiskers was used to study the responses of 44 single thalamic ventral posteromedial (VPM) neurons to dynamic and static stimulus components in urethane-anesthetized rats. The effects of local administration of the GABAA receptor antagonist, bicuculline, and the GABAB receptor antagonist, 2-hydroxysaclofen, were tested to determine whether and to what extent the responses altered when GABA-mediated inhibitory synaptic transmission was blocked. Two classes of phasically responding neurons were identified, ON/OFF and movement-sensitive types. Bicuculline enhanced the magnitudes of the responses from both types by 2.5-fold and ON/OFF responses were converted to movement-sensitive ones in 17 (43%) of the 40 ON/OFF neurons. 2-hydroxysaclofen either had no effect or appeared to act like a GABA agonist. In 21 (48%) neurons, a significantly reduced responsiveness was observed during a 100-ms period following the ON and OFF responses. This discharge suppression was especially prominent during the plateau phase of the stimulus, and in some cases extended for several 100 ms following its onset. This suppression was overcome neither by the GABA receptor antagonists, nor by ejection of AMPA or glutamate at currents that otherwise produced vigorous excitation. These results suggest that one functional role for GABAA-receptor-mediated synaptic inhibition in the somatosensory thalamus is the intramodal regulation of the form of expression of phasically responding neurons. Other thalamic inhibitory processes not mediated by GABAA or GABAB receptors that help to shape the expression of the responses of certain phasic neurons to maintained stimulation may exist. Overall, these mechanisms appear to mediate the precision of timing of thalamic neuronal firing in response to the rat's tactile environment.

Receptive fields and response properties of neurons in the star-nosed mole's somatosensory fovea.

Star-nosed moles have an extraordinary mechanosensory system consisting of 22 densely innervated nasal appendages covered with thousands of sensitive touch domes. A single appendage acts as the fovea and the star is constantly shifted to touch this foveal appendage to objects of interest. Here we investigated the receptive fields on the star and the response properties of 144 neurons in the mole's primary somatosensory cortex (S1). Excitatory receptive fields were defined by recording multiunit activity from the S1 representations of the nasal appendages that form the star, while stimulating the touch domes on the skin surface with a small probe. Receptive fields were among the smallest reported for mammalian glabrous skin, averaging <1 mm(2). The smallest receptive fields were found for the fovea representation, corresponding to its greater cortical magnification. Single units were then isolated, primarily from the representation of the somatosensory fovea, and the skin surface was stimulated with a small probe attached to a piezoelectric wafer controlled by a computer interface. The response properties of neurons and the locations of inhibitory surrounds were evaluated with two complementary approaches. In the first set of experiments, single microelectrodes were used to isolate unit activity in S1, and data were collected for stimulation to different areas of the sensory star. In the second set of experiments, a multi-electrode array (4 electrodes spaced at 200 microm in a linear sequence) was used to simultaneously record from isolated units in different cortical areas representing different parts of the sensory periphery. These experiments revealed a short-latency excitatory discharge to stimulation of the fovea followed by a long-lasting suppression of spontaneous activity. Sixty-one percent of neurons responded with an excitatory OFF response at the end of the stimulus; the remaining 39% of cells did not respond or were inhibited at stimulus offset. Stimulation of areas surrounding the central receptive field often revealed inhibitory surrounds. Forty percent of the neurons that responded to mechanosensory stimulation of the receptive field center were inhibited by stimulation of surrounding areas of skin on the same appendage. In contrast to neurons in rodent barrels, few neurons within a stripe representing an appendage responded to stimulation of neighboring (nonprimary) appendages on the snout. The small receptive fields, short latencies, and inhibitory surrounds are consistent with the star's role in rapidly determining the locations and identities of objects in a complex tactile environment.

Dynamic regulation of the siphon withdrawal reflex of Aplysia californica in response to changes in the ambient tactile environment.

Dynamic regulation of the siphon withdrawal reflex of Aplysia californica in response to changes in the ambient tactile environment.