Cortical processing of human somatic and visceral sensation.
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Somatic sensation can be localized precisely, whereas localization of visceral sensation is vague, possibly reflecting differences in the pattern of somatic and visceral input to the cerebral cortex. We used functional magnetic resonance imaging to study the cortical processing of sensation arising from the proximal (somatic) and distal (visceral) esophagus in six healthy male subjects. Esophageal stimulation was performed by phasic distension of a 2 cm balloon at 0.5 Hz. For each esophageal region, five separate 30 sec periods of nonpainful distension were alternated with five periods of similar duration without distension. Gradient echoplanar images depicting bold contrast were acquired using a 1.5 T GE scanner. Distension of the proximal esophagus was localized precisely to the upper chest and was represented in the trunk region of the left primary somatosensory cortex. In contrast, distension of the distal esophagus was perceived diffusely over the lower chest and was represented bilaterally at the junction of the primary and secondary somatosensory cortices. Different activation patterns were also observed in the anterior cingulate gyrus with the proximal esophagus being represented in the right midanterior cingulate cortex (BA 24) and the distal esophagus in the perigenual area (BA32). Differences in the activation of the dorsolateral prefrontal cortex and cerebellum were also observed for the two esophageal regions. These findings suggest that cortical specialization in the sensory-discriminative, affective, and cognitive areas of the cortex accounts for the perceptual differences observed between the two sensory modalities. (+info)
The role of the thalamic reticular neurons in alpha- and gamma-oscillations in neocortex: a mechanism for selective perception and stimulus binding.
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The long-term objective is to understand how large masses of neurons in the brain process information during various learning and memory paradigms. Both time- and space-dependent processes have been identified in animals through computer-based analytic quantifications of event-related extracellular potentials. New nonlinear analyses have been introduced that presume that the fine-grain variation in the signal is determined and patterned in phase-space. Some neurons in the primary visual cortex manifest gamma-band oscillations. These cells show both a nonspecific phase-alignment (response synchrony) and a specific tuning (orientation tuning) when stimuli are presented to their receptive fields. This dual regulation of the sensory cells is proposed to underlie stimulus binding, a theoretical mechanism for "object" perception. Nonlinear analytic results from gamma-activities in a simple model neuropil (olfactory bulb) suggest that neuroplasticity may arise through self-organization, a process in which a nonlinear change in the dynamics of the oscillatory field potentials is the hallmark. This self-organization may follow simple dynamical laws in which global cooperativity among the neurons is transiently brought about that, over trials, results in enduring changes in the nonlinear dynamics of some neurons. In conclusion, the sculpturing of the synaptic throughput in the sensory cortex (stimulus binding) may be associated with the irregular phases of the gamma-activities and may result from both specific and nonspecific systems operating together in a nonlinear self-organizing manner. (+info)
Insights into the functional specificity of the human corpus callosum.
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Patient VP underwent complete callosotomy for the control of intractable epilepsy at the age of 27 years. Subsequent MRI, however, revealed spared callosal fibres in the rostral and splenial ends of the corpus callosum. We report a series of experiments designed to determine whether these fibres support functional transfer of information between the two cerebral hemispheres. Although we found no evidence for transfer of colour, shape or size information, there is good evidence for transfer of word information. This suggests that the spared splenial fibres in VP's corpus callosum are material-specific. The results of these experiments illustrate the remarkable degree of functional specificity within the corpus callosum (+info)
Why are angles misperceived?
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Although it has long been apparent that observers tend to overestimate the magnitude of acute angles and underestimate obtuse ones, there is no consensus about why such distortions are seen. Geometrical modeling combined with psychophysical testing of human subjects indicates that these misperceptions are the result of an empirical strategy that resolves the inherent ambiguity of angular stimuli by generating percepts of the past significance of the stimulus rather than the geometry of its retinal projection. (+info)
Perception of bronchoconstriction and bronchial hyper-responsiveness in asthma.
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The inter-relationship between the perception of bronchoconstriction, bronchial hyper-responsiveness and temporal adaptation in asthma is still a matter of debate. In a total of 52 stable asthmatic patients, 32 without airway obstruction inverted question markforced expiratory volume in 1 s (FEV(1))/vital capacity (VC) 84.1% (S.D. 7.9%), and 20 with airway obstruction [FEV(1)/VC 60% (4%)], we assessed the perception of bronchoconstriction during methacholine inhalation by using: (i) the slope and intercept of the Borg and VAS (Visual Analog Scale) scores against the decrease in FEV(1), expressed as a percentage of the predicted value; and (ii) the Borg and VAS scores at a 20% decrease in FEV(1) from the lowest post-saline level (PB(20)). Bronchial hyper-responsiveness was assessed as the provocative concentration of methacholine causing a 20% fall in FEV(1) (PC(20)FEV(1)). The reduction in FEV(1) was significantly related to the Borg and VAS scores, with values for the group mean slope and intercept of this relationship of 0.13 (S.D. 0.08) and -1.1 (3.02) for Borg, and 1.5 (1.19) and -12.01 (35) for VAS. PB(20) was 3 (1.75) with Borg scores and 34.6 (20.5) with VAS scores. Compared with the subgroup without airway obstruction, the obstructed subgroup exhibited similar slopes, but lower Borg and VAS intercepts. For similar decreases in FEV(1) (5-20% decreases from the lowest post-saline values), the Borg and VAS scores were lower in the non-obstructed than in the obstructed subgroup. PC(20)FEV(1) was significantly related to both Borg PB(20) and VAS PB(20) when considering all patients. When assessing the subgroups, PC(20)FEV(1) was related to Borg PB(20) and VAS PB(20) in the non-obstructed subjects, but not in the obstructed subjects. In neither subgroup was the log of the cumulative dose related to the Borg and VAS scores at the end of the test. We conclude that, unlike in previous studies, the ability to perceive acute bronchoconstriction may be reduced as background airflow obstruction increases in asthma. Bronchial hyper-responsiveness did not play a major role in perceived breathlessness in patients without airway obstruction, and even less of a role in patients with obstruction. The cumulative dose of agonist did not appear to influence the perception of bronchoconstriction. (+info)
Perception of female reproductive state from vocal cues in a mammal species.
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While acoustic signalling by males is known to affect male-male competition, mate attraction and the timing of ovulation, the extent to which sexual selection has shaped the evolution of female acoustic signals is poorly understood. Among mammals, experimental evidence indicates that females attract mating partners by using olfactory and visual signals to advertise their reproductive state. Whether or not males ascertain female reproductive state from vocal signals has, however, never been systematically tested. In this study, we use playbacks of recorded vocalizations to demonstrate that male Barbary macaques, Macaca sylvanus, can discriminate between female copulation calls given at different stages of the oestrous cycle, responding more strongly to those given around the time when conception is most likely to occur. Acoustic analysis suggests that the mean dominant frequency of call units and a number of temporal parameters could provide males with the information necessary to discern the proximity of ovulation in this way Our results provide the first experimental evidence that the calls of female mammals may contain information on reproductive state, which males can perceive and use in such a way as to increase their reproductive success. (+info)
Screening techniques to identify people at high risk for diabetic foot ulceration: a prospective multicenter trial.
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OBJECTIVE: Diabetic foot ulceration is a preventable long-term complication of diabetes. A multicenter prospective follow-up study was conducted to determine which risk factors in foot screening have a high association with the development of foot ulceration. RESEARCH DESIGN AND METHODS: A total of 248 patients from 3 large diabetic foot centers were enrolled in a prospective study. Neuropathy symptom score, neuropathy disability score (NDS), vibration perception threshold (VPT), Semmes-Weinstein monofilaments (SWFs), joint mobility, peak plantar foot pressures, and vascular status were evaluated in all patients at the beginning of the study. Patients were followed-up every 6 months for a mean period of 30 months (range 6-40), and all new foot ulcers were recorded. The sensitivity, specificity, and positive predictive value of each risk factor were evaluated. RESULTS: Foot ulcers developed in 95 feet (19%) or 73 patients (29%) during the study. Patients who developed foot ulcers were more frequently men, had diabetes for a longer duration, had nonpalpable pedal pulses, had reduced joint mobility, had a high NDS, had a high VPT, and had an inability to feel a 5.07 SWE NDS alone had the best sensitivity, whereas the combination of the NDS and the inability to feel a 5.07 SWF reached a sensitivity of 99%. On the other hand, the best specificity for a single factor was offered by foot pressures, and the best combination was that of NDS and foot pressures. Univariate logistical regression analysis yielded a statistically significant odds ratio (OR) for sex, race, duration of diabetes, palpable pulses, history of foot ulceration, high NDSs, high VPTs, high SWFs, and high foot pressures. In addition, 94 (99%) of the 95 ulcerated feet had a high NDS and/or SWF which resulted in the highest OR of 26.2 (95% CI 3.6-190). Furthermore, in multivariate logistical regression analysis, the only significant factors were high NDSs, VPTs, SWFs, and foot pressures. CONCLUSIONS: Clinical examination and a 5.07 SWF test are the two most sensitive tests in identifying patients at risk for foot ulceration, especially when the tests are used in conjunction with each other. VPT measurements are also helpful and can be used as an alternative. Finally, foot pressure measurements offer a substantially higher specificity and can be used as a postscreening test in conjunction with providing appropriate footwear. (+info)
Towards identifying optimal doses for alpha-2 adrenergic modulation of colonic and rectal motor and sensory function.
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RATIONALE: Visceral sensation and motility are important in functional gut disorders and are partly controlled by adrenergic innervation. OBJECTIVES: To characterize the alpha2-adrenergic control of motor and sensory function of descending colon and rectum. METHODS: In 32 healthy volunteers, we assessed compliance, fasting and postprandial tone, and sensations of gas, urgency and pain during phasic distentions. Each subject received one agent at clinically approved doses: clonidine (0.05, 0.1, 0.2 or 0.3 mg p.o. ); or the alpha2 antagonist yohimbine (0.0125 mg, 0.05 mg, 0.125 mg or 0.2 mg intravenously and infusion over 2.5 h). RESULTS: Clonidine increased colonic and rectal compliance, and reduced tone, pain, gas sensation and rectal urgency. Clonidine showed large pairwise differences in sensation and motility between 0.05 and 0.1 mg doses, which did not interfere with the colon's motor response to feeding. Conversely, yohimbine dose-dependently altered the compliance curve, increased tone and sensations of gas, pain and urgency. Drug effects in the colon were more marked at low distensions; alpha2 modulation of rectal sensation was observed at all levels of distension. CONCLUSIONS: alpha2-adrenergic mechanisms modulate colorectal sensations and motility; at doses as low as 0.05 mg, clonidine reduced colorectal sensation while the tone response to feeding was preserved. These studies provide insight into the potential use of alpha2 agents in disease states. (+info)