Sensory Neurophysiology Research Articles

Neuropathophysiology of irritable bowel syndrome.

Widespread symptoms associated with the irritable bowel syndrome (IBS) are abnormal defecation and abdominal pain, both of which can be exacerbated by psychogenic stress. Disordered defecation may present as diarrhea or constipation. A subgroup of IBS patients alternate from one to the other over time. Urgency to stool often accompanies the diarrheal-state, and patients with the constipation-predominant form of IBS report straining and the feeling of incomplete evacuation. Basic scientific research aims for improved understanding of the physiology and pathophysiology of the digestive systems from which the arrays of IBS symptoms emerge. The key systems for the defecation-related symptoms are the intestinal secretory glands, the musculature, and the nervous system that controls and integrates their activity. Abdominal pain and discomfort arising from these systems adds the dimension of sensory neurophysiology. This review details current concepts of the underlying pathophysiology in terms of the physiology of intestinal secretion, motility, nervous control, sensing function, immuno-neural communication, and the brain-gut axis.

Tuning of cortical neurons to behaviorally salient acoustic signals

Your pet cat has run off somewhere. It's time to feed her, but she is nowhere to be found. You call for her, but she doesn't come. It's not the first time that this has happened. You wonder whether your cat is just playing hard to get, or perhaps she is just not neurally equipped to recognize and respond to your voice. Indeed, many animal species seem to depend on species-specific communication sounds for survival and social interactions. These acoustic signals are often unique and they can carry behaviorally relevant information that needs to be preferentially and expeditiously processed within the auditory system. A central issue in sensory neurophysiology is understanding how the auditory cortex differentially processes sounds that carry behavioral relevance to a specific species. Do auditory cortical neurons of some animal species respond more strongly to communication sounds produced by members of the same species as compared with sounds emanating from members of other species?A study by Wang and Kadia [1xDifferential representation of species-specific primate vocalizations in the auditory cortices of marmoset and cat. Wang, X. and Kadia, S.A. J. Neurophysiol. 2001; 86: 2616–2620PubMedSee all References[1] has confirmed this hypothesis. They obtained multi-unit extracellular recordings from the primary auditory cortices (area A1) of anesthetized cats and marmosets during audio playback of taped marmoset twitter calls. Marmosets are highly vocal primates that use twitter calls as part of their intra-species communicative repertoire during social interactions. These twitter calls consist of series of ‘phrases’ and they can be presented in a natural or reversed version, with the latter composed of reversed time courses of their amplitudes. In contrast to natural twitter calls, reversed marmoset calls have no behavioral relevance for cats and marmosets. Wang and Kadia reasoned that, because cats never encounter marmoset vocalizations in their acoustic environments, their auditory cortical neurons should fire less briskly when presented with marmoset twitter calls. By measuring the firing rates of A1 neurons, they found that neurons in cat A1 showed no preference for either natural or reversed marmoset calls. In contrast, neurons in marmoset A1 showed higher firing rates for natural, but not for reversed, marmoset calls. On average, marmoset A1 neurons showed mean firing rates that were twice as high as those of cat A1 neurons in response to natural twitter calls. Marmoset and cat A1 neurons responded about equally to time-reversed twitter calls, indicating that the auditory cortices in both species are capable of responding to sounds containing the acoustic complexities found in marmoset twitter calls. The authors concluded that marmoset A1 neurons displayed greater selectivity in their responses to natural marmoset calls than cat A1 neurons. Thus, species-specific, and perhaps also experience-dependent, mechanisms contribute to the processing of behaviorally relevant sounds in the auditory cortex of marmosets.These findings suggest the existence of species-specific neural mechanisms operating within the cerebral cortex to fine-tune the responsiveness of neurons to specific temporal patterns of stimuli. It is not yet clear whether additional factors, such as development and behavioral-sensory experience, play important roles in setting the neural template for the type of differential plasticity reported by Wang and Kadia. Numerous studies by M. Merzenich, A. Doupe and their colleagues have shown that other cortical areas, outside of A1, can display experience-dependent plasticity in their representational properties. It is not clear whether the neural circuitry within A1 is developmentally preprogrammed to selectively respond to vocal sounds of members of the same species. Experience probably plays a pivotal role in setting the response selectivity filters of A1 neurons.It would be interesting to test whether the species-specific responsiveness of A1 neurons can be ‘reprogrammed’ by repeated exposure to communication sounds emanating from members of other species. Also, on the cognitive level, does preferential firing of A1 neurons in response to intra-species vocal sounds encode intra-species recognition? On a less esoteric note, the answers to these questions might be gainfully applied to vocally coax uncooperative pets.

Cortical Responses to Single Mechanoreceptive Afferent Microstimulation Revealed with fMRI

The technique of intraneural microneurography/microstimulation has been used extensively to study contributions of single, physiologically characterized mechanoreceptive afferents (MRAs) to properties of somatosensory experience in awake human subjects. Its power as a tool for sensory neurophysiology can be greatly enhanced, however, by combining it with functional neuroimaging techniques that permit simultaneous measurement of the associated CNS responses. Here we report its successful adaptation to the environment of a high-field MR scanner. Eight median-nerve MRAs were isolated and characterized in three subjects and microstimulated in conjunction with fMRI at 3.0 T. Hemodynamic responses were observed in every case, and these responses were robust, focal, and physiologically orderly. The combination of fMRI with microstimulation will enable more detailed studies of the representation of the body surface in human somatosensory cortex and further studies of the relationship of that organization to short-term plasticity in the human SI cortical response to natural tactile stimuli. It can also be used to study many additional topics in sensory neurophysiology, such as CNS responses to additional classes of afferents and the effects of stimulus patterning and unimodal/crossmodal attentional manipulations. Finally, it presents unique opportunities to investigate the basic physiology of the BOLD effect and to compare the operating characteristics of fMRI and EEG as human functional neuroimaging modalities in an unusually specific and well-characterized neurophysiological setting.

General

The Journal of PhysiologyVolume 493, Issue suppl p. 35-42 Oral CommunicationFree Access General Motor & Sensory Neurophysiology First published: 01 December 1996 https://doi.org/10.1113/jphysiol.1996.sp021441AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Volume493, IssuesupplDecember 1, 1996Pages 35-42 RelatedInformation

Sensory neurophysiology of the cough reflex

The epithelium of the larynx, trachea, and larger bronchi contains sensory nerves that are responsible for cough. Their two main categories are rapidly adapting receptors (RARs) and C fiber receptors. Both types respond to a wide variety of mechanical and chemical irritants. The RARs are the main sensory complex responsible for cough. C fiber receptors cause neurogenic inflammation by the release of tachykinins such as substance P. The reflex action of C fiber receptors seems to be inhibition of cough. However, the released tachykinins can stimulate RARs and promote or enhance the cough response. The strength and pattern of cough depends on the sites of the airway that are stimulated and the local and central reflex interactions of the RARs and C fiber receptors. Tachykinins seem to be involved in cough, but their role needs further study. (J A LLERGY C LIN I MMUNOL 1996;98:S84-90.)

Sensory neurophysiology of the cough reflex

<h2>Abstract</h2> The epithelium of the larynx, trachea, and larger bronchi contains sensory nerves that are responsible for cough. Their two main categories are rapidly adapting receptors (RARs) and C fiber receptors. Both types respond to a wide variety of mechanical and chemical irritants. The RARs are the main sensory complex responsible for cough. C fiber receptors cause neurogenic inflammation by the release of tachykinins such as substance P. The reflex action of C fiber receptors seems to be inhibition of cough. However, the released tachykinins can stimulate RARs and promote or enhance the cough response. The strength and pattern of cough depends on the sites of the airway that are stimulated and the local and central reflex interactions of the RARs and C fiber receptors. Tachykinins seem to be involved in cough, but their role needs further study. (J ALLERGY CLIN IMMUNOL 1996;98:S84-90.)

Specificity of mono- and divalent salt transduction mechanisms in frog gustation evidenced by cobalt chloride treatment

1. Discrimination among stimuli with similar physical properties represents a formidable problem in sensory neurophysiology. The differential effect of cobalt chloride treatment on gustatory responses to monovalent and divalent salts may help to explain aspects of how the frog gustatory system encodes these stimuli. 2. Gustatory neural responses recorded from the glossopharyngeal nerve to divalent stimuli (CaCl2 and MgCl2) were inhibited by CoCl2 treatment, whereas monovalent responses (NaCl and KCl) were greatly augmented. Both effects were highly significant and completely reversible. 3. Intracellular recordings from the gustatory receptor cells, which synaptically initiate the impulses in the glossopharyngeal afferents, imply that these neural events are not a simple reflection of the receptor potential magnitude. Monovalent receptor potentials magnitudes (millivolts of depolarization) were enhanced by cobalt chloride, but receptor potentials to divalent stimuli were not inhibited. Rather they were either unaffected (MgCl2) or augmented (CaCl2). 4. Membrane resistance change during salt stimulation with cobalt chloride treatment followed the qualitative pattern observed with the neural response. Membrane resistance (in megohms) of the receptor cell was greater for divalent stimuli with cobalt treatment compared with divalent stimuli alone. Membrane resistance changes for monovalent stimuli were less with cobalt treatment compared with monovalent stimuli alone. These observations indicate that the glossopharyngeal neural response is not a simple reflection of the magnitude of the receptor potential but must be considered in conjunction with membrane resistance as an indicator of synaptic transmission. 5. These data were interpreted in terms of leading models of salt taste transduction, i.e., adsorption theories, phase boundary theories, and the direct penetration theories. Relevant mechanistic considerations for salt taste transduction in the frog include binding by divalents to membrane surface changes and amiloride-sensitive monovalent cation channels. It was concluded that the surface potential alone was not a critical variable in the mechanism of cobalt chloride alteration of salt responses.

Gustatory neural processing in the hindbrain.

Sensory neurophysiology must account for sensation and perception. Given the richness and complexity of our auditory and visual worlds, this remains a daunting charge even after decades of sophist icated visual and auditory neurophysiology. Taste, on th� other hand, should be easy. It contains little of the spatial and tempQral dimensions found in vision, audition, or somesthesis, and humans report only a few taste categories or qualities. In English, the most common are sweet, salty, sour , and bitter . Given this apparently simpler task, how does gustatory neurophysiology acquit itself? Gustatory neurophysiological data, primarily from rodents, match human quality judgments moderately well, but the degree of this success or failure depends upon the theoretical bias of the beholder , as well as on the scope of the gustatory responses included. Taste per se may have only a few sensory categories, but other attributes contribute complexity and richness to the sensory experience that leaves present neurophysiological data far behind. The absence of obvious stimulus dimensions continues to impede neuro­ physiological analysis of gustatory sensibility. The molecules that elicit similar verbal reports of taste from humans and neural activity in gustatory afferent nerves often bear little chemical relation to one another . Sugars,

Sensory cortex and the mind-brain problem

AbstractOne of the implicit, and sometimes explicit, objectives of modern neuroscience is to find neural correlates of subjective experience so that different qualities of that experience might be explained in detail by reference to the physical structure and processes of the brain. It is generally assumed that such explanations will make unnecessary or rule out any reference to conscious mental agents. This is the classic mind-brain reductivist program. We have chosen to challenge the optimism underlying such an approach in the context of sensory neurophysiology and sensory experience. Specifically, we ask if it is possible to explain the subjective differences among seeing, hearing, and feeling something by inspecting the structure and function of primary visual, auditory, and somesthetic cortex.After reviewing the progress in localization of sensory functions over the past two centuries and examining some aspects of the structure and function of somesthetic, auditory, and visual cortex, we infer that one cannot explain the subjective differences between sensory modalities in terms of present day neuroscientific knowledge. Nor do present trends in research provide grounds for optimism.At this point we turn to three philosophical theories to see what promise they hold of explaining these differences. A brief discussion of each – identity theory, functionalism, and eliminative materialism – suggests that none adequately accounts for the facts of the situation, and we tentatively conclude that some form of dualism is still a tenable hypothesis.

The Neurophysiology of Information Processing and Cognition

In the first textbook of physiological psychology in 1874, Wundt (128) expressed his conviction that the central problem of the field was the analysis of the physiologi­ cal bases of consciousness and subjective experience. Two generations later, the behaviorist movement, motivated partly by the excesses of introspective psychology and partly by imitation of operationalism in physics, succeeded in exorcizing both the language of conscious experience and the study of consciousness and mental states. Ever since, the dominant trend in studies of learning, including the neuro­ physiology of learning, has followed a strict behaviorist line. Reductionist ap­ proaches, such as the measurement of habit strengths and response rates and the tracing of neural circuits, have led to the accumulation of a vast amount of empirical knowledge but little insight into basic mechanisms. Sensory neurophysiology has followed a similar philosophical and methodological program, culminating for some in the extreme position that entire percepts may be represented by the firing of one or a few neurons (3, 69), or that higher order perceptual and cognitive functions are represented in localized anatomical regions. However, the study of how univariate sensory features, or stimulus attributes, differentially affect various anatomical structures ignores the problem of how the organism constructs an integrated, mul­ tivariate, and multidimensional perception of its environment.

Sensory re-education after median nerve lesions

Technique for re-educating sensory function after median nerve lesions at the wrist is described. Results of re-education of Twenty-three patients are presented. The functional results are good and belie the traditional view of sensory function after nerve suture. Recent advances in sensory neuro-physiology are discussed which may explain the successes of this technique.