Cortical barrel field ablation and unconditioned whisking kinematics

The effects of "barrel cortex" ablation upon the biometrics of "exploratory" whisking were examined in three head-fixed rats which had previously sustained unilateral ablation of the left cortical "barrel field" under electrophysiological control. Unconditioned movements of a pair of bilaterally homologous whiskers (C-1, Right, Left) were monitored, optoelectronically, with other whiskers present. Whisking movements on the intact and ablated side were analyzed with respect to kinematics (protraction amplitude and velocity) whisking frequency and phase relationships between whisking movement on the two sides of the face. Histological analysis confirmed complete removal of S-1 "barrel cortex". In normal animals whisking movements have a characteristic rhythm (6-9 Hz), and protractions on the two sides of the face tend to be both synchronous and of very similar amplitudes. In the lesioned animals, whisking frequency was unchanged and whisking movements remained bilaterally synchronous. However, there was a significant difference between the amplitude of Right and Left whisker movements which was evident many months postoperatively. Our results suggest that the deficits in vibrissa-mediated tactile discrimination reported after "barrel" field ablation may reflect an impairment in the animal's ability to modulate whisking parameters on the two sides of the face to meet the functional requirements of a discriminative whisking task. The effects upon whisking amplitude seen after unilateral barrel field ablation are consistent with a model in which the activity of a whisking Central Pattern Generator is modulated by descending inputs to achieve sensorimotor control of whisking movement parameters.

Temporal organization of multi-whisker contact in rats

Previous work has established that during exploration and discrimination, rats move their whiskers at frequencies between 6 and 12 Hz and that whisking frequency changes during contact. One critical component of any tactile system is contact. In the rat whisker system, such contacts may involve one or more vibrissa in the whisker array and contact duration of each whisker may vary over a considerable range, depending upon the behavioral context. However, little is known about the variables controlling contact duration or about the temporal relationships among contacts by adjacent whiskers. To address these issues head fixed rats were trained to touch a piezo-contact-sensor with the shaft of their whiskers (Bermejo and Zeigler, Somatosens Mot Res 17: 373-377, 2000). During the task, whisker movements and contacts were monitored with a high-speed camera at 500 frames/s and stored on videotape. To facilitate analysis, animals had their whiskers selectively trimmed. Data are reported from animals with C1 & C2, D1 & D2, or Arc2 (E2, D2, C2, B2) whiskers intact. For both row and arc animals, when just a single whisker touched the sensor the duration of contact was significantly shorter than when multiple whiskers made contact. When multiple whiskers made contact, onset was rarely simultaneous. Furthermore, in row-intact animals, contact progressed in an orderly fashion such that the rostral whisker in a row made contact first followed 24 ms (SE = 1.9 ms) later by the caudal whisker. When contact reversed the caudal whisker lifted off first, followed by the rostral whisker. Thus, the order in which whiskers touch an object regulates contact duration: the first whisker to touch the sensor stays in contact longer than any other whisker. The temporal discharge properties of neurons in the trigeminal system are expected to reflect position of whiskers on the nose.

Feeling touches in someone else's hand

Cerebral damage may induce a delusional belief so that patients claim that their limbs contralateral to the side of the lesion belong to someone else (somatoparaphrenia). This disorder, which is not due to a general delirium, is frequently accompanied by the inability to feel tactile sensations in the 'non-belonging' part of the body. We report the unique case of a patient with somatoparaphrenia in whom dense tactile imperception in the left hand dramatically recovered when she was instructed to report touches delivered to her niece's hand, rather than to her own hand. We suggest that, through this verbal instruction, the mismatch between the patient's belief about the ownership of her left hand and her ability to perceive touch on it was transiently recomposed. This is evidence that apparently elementary deficits, such as hemianesthesia, and selective delusional behavior, such as somatoparaphrenia, may both originate from an impairment of the body image.

Remodeling of somotasensory hand representations following cerebral lesions in humans

There is evidence of reorganization of somatotopic maps following cortical lesions in mammals such as monkeys, raccoons and rats. However, there has been a striking lack of research on somatosensory plasticity following cerebral damage in adult humans. We describe two individuals with left hemisphere damage who misperceive the locations of tactile stimuli whose presence or absence they can readily detect. We find that the mislocalizations preserve the relative topography of pre-lesion experiences, resulting in shifted and compressed representations of the hand surfaces. These results not only provide evidence for systematic remodeling of somatotopic maps in humans, they also reveal that the systematic changes in cortical topography that have been documented using electrophysiological methods may give rise to similarly systematic changes in somatosensory perception itself.

Perceptual changes in the anterior maxilla after placement of endosseous implants

BACKGROUND

The innervation of skin and oral mucosa plays a major physiologic role in exteroception. It is also of interest clinically, as illustrated by sensory changes after neurosurgical procedures.

PURPOSE

The goal of this study was to assess the perception of mechanical stimuli applied to the anterior maxilla in denture wearers and subjects rehabilitated with osseointegrated implants compared with that in subjects with a natural dentition.

MATERIALS AND METHODS

Five groups of subjects were selected and tested in the maxillary region only. Test groups included patients with a complete denture, an implant-supported fixed prosthesis (full or partial), or a single-tooth replacement. Light-touch sensation and two-point discrimination were performed on the buccal side of the alveolar mucosa and vibrotactile function was determined for natural teeth, full dentures, or implant-supported prostheses.

RESULTS

For light-touch sensation, no significant differences could be found between the groups. For two-point discrimination, full-denture patients showed higher threshold levels than the other groups. The threshold levels for vibrotactile function were higher in both full dentures and implant-supported prostheses compared with natural dentitions.

CONCLUSION

Natural dentitions offer superior vibrotactile function compared to any other dental status. Full dentures often show a stronger deterioration of the (vibro)tactile function compared with implant-supported prostheses.

Spatial attention and crossmodal interactions between vision and touch

In the present paper, we review several functional imaging studies investigating crossmodal interactions between vision and touch relating to spatial attention. We asked how the spatial unity of a multimodal event in the external world might be represented in the brain, where signals from different modalities are initially processed in distinct brain regions. The results highlight several links between visual and tactile spatial representations. First, we found that activity in the anterior part of the intraparietal sulcus was influenced by stimulus position independently of the modality of the stimulation. This is consistent with crossmodal interactions via sensory convergence from early modality-specific spatial maps to higher-order multimodal regions. Second, we found that stimulation in, or attention to, one modality could affect activity in areas dedicated to a different modality, in a spatially-specific manner. These spatial crossmodal effects in unimodal regions demonstrate congruous activity in anatomically distant brain areas that represent similar external locations, implicating a distributed network of spatial representations in crossmodal integration. Finally, the results suggest that the temporo-parietal junction may be involved in aspects of controlling spatial attention, for both vision and touch. A multimodal attentional system may influence activity in distinct brain areas representing common regions of space for different modalities, thus suggesting a link between spatial attention and crossmodal integration.

Crossmodal links in spatial attention between vision, audition, and touch: evidence from event-related brain potentials

Results from event-related potential (ERP) studies are reviewed that investigated crossmodal links in spatial attention between vision, audition and touch to find out which stages in the processing of sensory stimuli are affected by such crossmodal links. ERPs were recorded in response to visual, auditory, and tactile stimuli under conditions where attention was directed to a specific location within one (primary) modality, while stimuli in another (secondary) modality were to be ignored regardless of their position. Systematic ERP effects of spatial attention were observed not only in the primary modality, but also for secondary modality stimuli, thus revealing crossmodal links in spatial attention. These links affected relatively early sensory-specific ERP components between 100 and 200 ms post-stimulus. Beyond 200 ms, ERPs to secondary modality stimuli were little affected by the current focus of attention within another modality. This pattern of results suggests that crossmodal links in spatial attention may affect sensory-perceptual processes within modality-specific cortical regions, but have little impact on later post-perceptual processing stages.

The non-classical auditory pathways are involved in hearing in children but not in adults

Auditory information ascends through the brainstem to the cerebral cortices in two parallel pathways, known as the classical and the non-classical ascending auditory pathways. The importance of the non-classical auditory pathway for hearing in humans is unknown but its subcortical connection to limbic structures may be important in tinnitus. In this study we show evidence that non-classical pathways are involved in loudness perception in young individuals but not in adults. We used the fact that some neurons in the non-classical auditory pathways receive somatosensory input and we determined the effect on loudness perception of monaural sounds from electrical stimulation of the median nerve at the wrist. Stimulation of the somatosensory system had the greatest effect on loudness perception in the youngest children that we studied (7-8 years) and the effect was minimal for individuals above 20 years of age. The effect was an increase in loudness in 20 of the 40 individuals we studied and a decrease in 4 individuals; 16 experienced no noticeable change in loudness during somatosensory stimulation.

Vision modulates somatosensory cortical processing

Over 150 years ago, E.H. Weber declared that experience showed that tactile acuity was not affected by viewing the stimulated body part. However, more recent investigations suggest that cross-modal links do exist between the senses. Viewing the stimulated body site improves performance on tactile discrimination and detection tasks and enhances tactile acuity. Here, we show that vision modulates somatosensory cortex activity, as measured by somatosensory event-related potentials (ERPs). This modulation is greatest when tactile stimulation is task relevant. Visual modulation is not present in the P50 component reflecting the primary afferent input to the cortex but appears in the subsequent N80 component, which has also been localized to SI, the primary somatosensory cortex. Furthermore, we replicate previous findings that noninformative vision improves spatial acuity. These results are consistent with a hypothesis that vision modulates cortical processing of tactile stimuli via back projections from multimodal cortical areas. Several neurophysiological studies suggest that primary and secondary somatosensory cortex (SI and SII, respectively) activity can be modulated by spatial and tactile attention and by visual cues. To our knowledge, this is the first demonstration of direct modulation of somatosensory cortex activity by a noninformative view of the stimulated body site with concomitant enhancement of tactile acuity in normal subjects.

Cortical and thalamic connections of the parietal ventral somatosensory area in marmoset monkeys (Callithrix jacchus)

Microelectrode mapping methods were used to define the parietal ventral somatosensory area (PV) on the upper bank of the lateral sulcus in five marmosets (Callithrix jacchus). In the same animals, neuroanatomical tracers were placed into electrophysiologically identified sites in PV and/or the second somatosensory area (S2). Foci of anterograde and retrograde label were related to electrophysiological maps of cortical areas and cortical and thalamic architecture. The results lead to the following conclusions: (1) Multiunit recordings from cortex on the upper bank of the lateral sulcus demonstrate that PV is somatotopically organized, with the face representation adjoining area 3b and the hindlimb and tail representations away from this border in cortex deep on the upper bank of the lateral sulcus. The forelimb representation is caudal in PV adjacent to the S2 forelimb representation. The body surface representation in PV approximates a mirror image of that in S2; (2) Areas PV and S2 are less myelinated and have less cytochrome oxidase enzyme activity than area 3b; (3) The ventroposterior inferior nucleus (VPI) of the thalamus provides the major somatosensory projections to PV. PV is reciprocally connected with VPI and anterior pulvinar; (4) PV has ipsilateral cortical connections with areas 3a, 3b, 1, and M1 and higher order somatosensory fields, and at least most of these connections are somatotopically matched; and (5) Callosal connections of PV are with S2 and PV of the other cerebral hemisphere. These results further establish PV as one of at least four somatosensory areas of the lateral sulcus of primates.

The influence of selective grinding on the thickness discrimination threshold of patients wearing complete dentures

The influence of selective grinding on the ability of patients wearing complete dentures to discriminate thicknesses occlusally was evaluated. The study included two groups of white Caucasian patients, matched for age, sex and duration of edentulism; 12 wearing traditional complete dentures and 12 wearing maxillary complete denture and mandibular implant-retained overdenture (MIR-OVD). The ability to discriminate thickness was evaluated before and after selective grinding. In both groups, sensitivity improved after selective grinding. Subjects wearing MIR-OVD showed a better ability to discriminate thickness than those rehabilitated with traditional complete dentures. The thickness discrimination threshold might be a suitable method to evaluate complete dentures fit.

Somatosensory cortical neuronal population activity across states of anaesthesia

Experiments were carried out to learn about changes in sensory cortical processing associated with different levels of anaesthesia. Traditionally this question has been addressed by studying single neurons. Because state changes are likely to influence the relationships between neurons, the present experiments were undertaken to investigate the spatial and temporal firing patterns distributed across cortex. Using 5 x 5 or 10 x 10 microelectrode arrays, spontaneous and stimulus-evoked activity of multineuron clusters was recorded from rat somatosensory 'barrel' cortex (the whisker representation) during a light surgical stage of urethane anaesthesia, and after two supplemental doses of urethane which led to intermediate and deep levels of anaesthesia. At all depths of anaesthesia, spontaneously occurring action potentials at a single electrode tended to be clustered into 'bursts.' With increasing anaesthetic depth, bursts became more prominent and rhythmic, and increasingly synchronized between cortical barrel-columns. Burst frequency decreased and fewer spikes occurred outside bursts, leading to a decrease in the overall spontaneous firing rate. The cortical territory engaged by individual whiskers contracted with increasing depth of anaesthesia, leading to the spatial segregation of whisker representations. At all stages of anaesthesia, whisker stimulation produced the maximal cortical response when delivered close to burst onset. These observations show that ongoing spontaneous activity modulates sensory response properties and makes peripheral tactile information accessible to a cortical territory whose size is determined by the phase of burst cycle. The possible significance of the cyclic cortical responsiveness encountered during urethane anaesthesia to cortical processing in awake rats is considered.

Cortical neuronal ensembles driven by dorsal horn spinal neurones with spontaneous activity in the cat

Simultaneous recordings of cortical activity, recorded as the cortical local field potential (CLFP) in the contralateral posterior sigmoid gyrus, and the spinal activity, recorded as the cord dorsum potential (CDP) of the L6 lumbar segment, were made in the anaesthetized cat. The electrodes were positioned in somatosensory regions where the largest spontaneous negative CLFPs and CDPs were recorded. We found that spontaneous negative CLFPs were preceded by spontaneous negative CDPs with a mean latency of 14.4+/-3.5 ms. Amplitude of these spontaneous negative CLFPs was abolished after section of the dorsal columns and ipsilateral dorsolateral funiculus. It is concluded that the neurones of the primary somatosensory cortex can be driven by dorsal horn spinal neurones producing the spontaneous negative CDPs. This suggests very strongly that spontaneous neuronal activity in somatosensory regions of the brain is generated not only by ongoing activity of neurones located at supraspinal sites, but also by ongoing activity of spinal neurones.

Self-induced versus reactive triggering of synchronous movements in a deafferented patient and control subjects

The present study investigates the contribution of tactile-kinesthetic information to the timing of movements. The relative timing of simultaneous tapping movements of finger and foot (hand-foot asynchrony) was examined in a simple reaction time task and in discrete self-initiated taps (Experiment 1), and in externally triggered synchronization tapping (Experiment 2). We compared the performance of a deafferented participant (IW) to the performance of two control groups of different ages. The pattern of results in control groups replicates previous findings: Whereas positive hand-foot asynchronies (hand precedes foot) are observed in a simultaneous reaction to an auditory stimulus, hand-foot asynchronies are negative with discrete self-initiated as well as auditorily paced sequences of synchronized finger and foot taps. In the first case, results are explained by a simultaneous triggering of motor commands. In contrast, self-initiated and auditorily paced movements are assumed to be controlled in terms of their afferent consequences, as provided by tactile-kinesthetic information. The performance of the deafferented participant differed from that of healthy participants in some aspects. As expected on the basis of unaffected motor functions, the participant was able to generate finger and foot movements in reaction to an external signal. In spite of the lack of movement-contingent sensory feedback, the deafferented participant showed comparable timing errors in self-initiated and regularly paced tapping as observed in control participants. However, in discrete self-initiated taps IW's hand-foot asynchronies were considerably larger than in control participants, while performance did not differ from that of controls in continuous movement generation. These findings are discussed in terms of an internal generation of the movement's sensory consequences (forward-modeling).

The evaluation of skin friction using a frictional feel analyzer

BACKGROUND/AIMS

Sensory evaluation is an important factor for cosmetic products. Several devices for the measurement of sensory properties have been developed in recent years. The objective here is to measure skin surface friction using these devices and examine the correlation with other physiological parameters in order to evaluate the potential of physical measurement of tactile sensation.

METHODS

A KES-SE Frictional Analyzer, a commercial device for measurement of surface frictional characteristics, was used in this study. An arm holder was added to this device for measurement on the human forearm. The frictional coefficient (MIU) and its mean deviation (MMD) were used as the parameter to indicate surface friction. The moisture content in the stratum corneum was measured with a Corneometer CM825, the transepidermal water loss with a Tewameter TM210, the viscoelastic properties of the skin with a Cutometer SEM575 and the skin surface pattern by observing the negative replica using silicon rubber.

RESULTS

The MIU was not influenced by load; however, it was increased due to water application on the skin. The relationship between MIU and the moisture content in the stratum comeum, between MMD and skin surface pattern and between MMD and viscosity of both normal human forearm skin and SDS (sodium dodecyl sulfate)-induced dry skin were confirmed by statistical analysis in a test on human subjects. There was also a correlation between either MIU or MMD and sensory evaluation in the morning after the application of moisturizing products.

CONCLUSION

Human skin surface friction was measured by using a KES-SE Frictional Analyzer. Judging from the correlation between either MIU or MMD and sensory evaluation, we considered this instrumental analysis to be useful for evaluating the tactile impression of human skin.

Magnitude estimation of tangential force applied to the fingerpad

Prior research on large-fibre skin mechanoreceptors in humans and monkeys has demonstrated their sensitivity to perpendicular skin indentation and to the rate of force application. Although some studies have examined skin afferent responses to stretch, relatively few investigations have examined the neural and perceptual correlates of shear forces applied tangentially to the skin. The present study assessed the ability of human subjects to scale different levels of tangential force applied to the distal pad of the index finger. Subjects were instructed to choose their own magnitude estimation scale. Seven force levels ranging from 0.15 to 0.70 N were delivered randomly at rates of 0.10 N/s, 0.15 N/s or 0.30 N/s. Tangential forces were produced with a smooth metal spatula coated with an adhesive to insure a shear force on the underlying skin without slip. The same procedures were also used to generate skin indentation with normal forces. The results showed that most human subjects were able to scale different magnitudes of both tangential and normal forces applied to the tip of the index finger. The rate of force change did not influence the perception of the applied forces. These results highlight the potentially important role of tangential forces in haptic perception.

A unique area of the homonculus: the topography of the primary somatosensory cortex in humans following posterior scalp and shoulder stimulation

We recorded somatosensory evoked magnetic field (SEF) to investigate the differentiation in the receptive area for the face, lower part of the posterior scalp (mastoid) and shoulder, which occupy an unique area in the homunculus. We analyzed the location of the equivalent current dipole (ECD) of SEF following electrical stimulation of the skin at the face, mastoid and shoulder in 20 normal subjects. Three deflections (1M, 2M and 3M) were obtained within 50 ms of the stimulation in 16 of 20 subjects. The peak latency of the 1M and 2M was not significantly different at any stimulus sites. The amplitude of the 1M was significantly larger following the face than mastoid stimulation (p<0.05). The 16 subjects were classified according to the locations of the ECD on stimulation of the mastoid: close to that for shoulder stimulation, but significantly (p<0.05) more superior and medial to that following the face stimulation (Type 1, eleven subjects); close to that for face stimulation, but significantly (P<0.05) more inferior and lateral to that following the shoulder stimulation (Type 2, five subjects). The site of the receptive area for the posterior scalp shows interindividual variation, possibly due to anatomical differences.

Humans integrate visual and haptic information in a statistically optimal fashion

When a person looks at an object while exploring it with their hand, vision and touch both provide information for estimating the properties of the object. Vision frequently dominates the integrated visual-haptic percept, for example when judging size, shape or position, but in some circumstances the percept is clearly affected by haptics. Here we propose that a general principle, which minimizes variance in the final estimate, determines the degree to which vision or haptics dominates. This principle is realized by using maximum-likelihood estimation to combine the inputs. To investigate cue combination quantitatively, we first measured the variances associated with visual and haptic estimation of height. We then used these measurements to construct a maximum-likelihood integrator. This model behaved very similarly to humans in a visual-haptic task. Thus, the nervous system seems to combine visual and haptic information in a fashion that is similar to a maximum-likelihood integrator. Visual dominance occurs when the variance associated with visual estimation is lower than that associated with haptic estimation.

Electrophysiological evidence for trigeminal neuron sensitization in patients with migraine

The electrically elicited corneal reflex is a useful tool for exploring the trigeminal system in humans and it may provide additional evidence pointing to a dysfunction of this system in migrainous patients. Tactile perception, corneal reflex and pain thresholds were studied in 48 migraine without aura patients during pain-free periods and compared with those observed in 24 controls. Twenty-eight of the patients had strictly unilateral headache, while the other 20 had bilateral or side-shifting pain during attacks. Both migraine subgroups (bilateral and unilateral) showed significantly lower thresholds compared with controls. The lowest values were observed on the symptomatic side of unilateral migraine patients. These findings suggest that sensorimotor mechanisms and/or pain control systems at the trigeminal level are impaired in migraine. The bilateral location of these abnormalities seems to point to a centrally located dysfunction.

Response characteristics of cutaneous mechanoreceptors in neuropathic rats

The activity of single myelinated afferents was recorded from dorsal roots L4-5 in normal Sprague-Dawley rats and animals that developed mechanical hypersensitivity following ischemic injury to the sciatic nerve. The mechanical response properties and conduction velocity of afferents conducting through the injury site (about 50% of units) were similar to controls. However, the majority of afferents not conducting through the injury site exhibited ongoing activity. The results suggest that mechanical allodynia may be at least partly due to the central integration of activity arising from these two populations of afferents in neuropathic rats.

Expression of c-Fos, Fos B, Jun B, and Zif268 transcription factor proteins in rat barrel cortex following apomorphine-evoked whisking behavior

Apomorphine-evoked expression of transcription factor proteins: c-Fos, Fos B, Jun B, and Zif268 (also named Krox-24, NGFI-A, Egr-1), was investigated in rat somatosensory (barrel) cortex. The effect of the N-methyl-D-aspartate receptor antagonist MK-801 on their expression was also analyzed. Apomorphine is a dopamine receptor agonist, eliciting motor activity, including enhanced whisking leading to the activation of vibrissae representation in the barrel cortex. Rats had their whiskers clipped on one side of the snout. The Zif268 levels were markedly reduced by this procedure alone. In contrast, apomorphine (5.0 mg/kg) evoked marked c-Fos elevation, less pronounced changes in Jun B and Zif268 and no change in Fos B. The greatest apomorphine-evoked c-Fos accumulation was observed in layers IV and V/VI of non-deprived barrel cortex and was not significantly influenced by MK-801 injection at 0.1 mg/kg. A higher dose of MK-801 (1.0 mg/kg) produced abnormalities in locomotor behavior and diminished c-Fos levels on the non-deprived side to the ones observed in the sensory stimulus-deprived cortex. We conclude that the response of the somatosensory cortex is selective with respect to both the gene activated and its cortical layer localization. Furthermore, sensory stimulation provides a major but not the only component to apomorphine-evoked barrel cortex gene activation.

Insulin-like growth factor-1 improves somatosensory function and reduces the extent of cortical infarction and ongoing neuronal loss after hypoxia-ischemia in rats

Treatment with insulin-like growth factor-1 has been demonstrated to reduce the extent of cortical infarction 5 days after hypoxic-ischemic brain injury. As neuronal death can be progressive and long lasting after initial injury, the present study examined the long-term effects of insulin-like growth factor-1 on late neuronal loss 20 days after hypoxic-ischemic injury, together with evaluating neurobehavioral outcome as assumed by somatosensory function. Unilateral brain injury was induced in adult rats by carotid artery ligation followed by 10 min of hypoxia (6% O2). A single dose of insulin-like growth factor-1 (50 microg) was administered intracerebroventricularly via a stereotaxically pre-fixed cannula 2 h after injury. A bilateral tactile stimulation test was used to examine the degree of somatosensory function at 3, 5, 10 and 20 days after the hypoxia in both insulin-like growth factor-1- (n=12) and its vehicle- (n=12) treated rats, along with sham-operated rats (n=9). Cortical infarction and percentage of selective neuronal loss in the cerebral cortex were examined 20 days after the hypoxic-ischemic injury in both treatment groups. Hypoxic-ischemic injury resulted in a significant delay in the time taken to contact the patch over the period examined (left/right ratio 5.1+/-0.79), particularly at 3 days (7.0+/-2.8) after the hypoxia, compared to sham-operated rats (1.1+/-0.9, P<0.05). The overall effect of insulin-like growth factor-1 in reducing the time taken to contact the patch was significant (P=0.03, 2.6+/-0.79) compared to the vehicle group. There was a trend towards a reduction of cortical infarction after insulin-like growth factor-1 treatment (P=0.058), however insulin-like growth factor-1 significantly reduced the percentage of selective neuronal loss (P=0.027) 20 days following the hypoxia. From these data we suggest that insulin-like growth factor-1 improves somatosensory function by reducing both the extent of cortical infarction and ongoing progressive neuronal death during brain recovery from hypoxic-ischemic injury.

von Frey hairs: new materials for a new design

von Frey filaments are widely used in pain research. Conventionally, they are made of synthetic fibres. This plastic material is susceptible to changes in humidity and temperature, and such filaments do not keep their calibration. Filaments made of optical glass fibres are highly elastic and do not suffer these problems. Their optical properties can be used to make thin fibres more visible.

A review and evaluation of research on the deaf-blind from perceptual, communicative, social and rehabilitative perspectives

This paper reviews research on deaf-blind individuals, primarily from behavioral and communicative points of view. Inclusion in the population of deaf-blind is qualified by describing a variety of subgroups and genetically based syndromes associated with deaf-blindness. Sensory assessment procedures--based primarily on residual capacities--are appraised. Consequences for everyday life are described briefly. Non-sensory, alternative classificatory schemes and procedures are presented and the results from behavior modification procedures used for correcting maladaptive behaviors are summarized. Methods for communicating tactilely are described and evaluated. Attention is also drawn to some suggestions regarding learning of alphabetic codes and sign acquisition. Finally, suggestions for future research are proposed.