Haptic synthesis of shapes and sequences.
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Haptic perception of shape is based on kinesthetic and tactile information synthesized across space and time. We studied this process by having subjects move along the edges of multisided shapes and then remember and reproduce the shapes. With eyes closed, subjects moved a robot manipulandum whose force field was programmed to simulate a quadrilateral boundary in a horizontal plane. When subjects then reproduced the quadrilateral using the same manipulandum, with eyes still closed but now with the force field set to zero, they made consistent errors, overestimating the lengths of short segments and underestimating long ones, as well as overestimating acute angles and underestimating obtuse ones. Consequently their reproductions were more regular than the shapes they had experienced. When subjects felt the same quadrilaterals with the same manipulandum but drew them on a vertical screen with visual feedback, they made similar errors, indicating that their distortions reflected mainly perceptual rather than motor processes. In a third experiment, subjects explored the 3 sides of an open shape in a fixed order. The results revealed a temporal pattern of interactions, where the lengths and angles of previously explored segments influenced the drawing of later segments. In all tasks, our subjects were as accurate as subjects in earlier studies who haptically explored only single lines or angles, suggesting that the mental processes that synthesize haptic data from multiple segments into complete shapes do not introduce any net error. (+info)
Behavioural therapy (biofeedback) for solitary rectal ulcer syndrome improves symptoms and mucosal blood flow.
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AIMS: The aim of the study was to determine if there is a permanent disorder of mucosal blood flow in patients with solitary rectal ulcer syndrome (SRUS) or a disorder related to autonomic gut innervation and physiological function that is reversible concomitant with successful treatment. Rectal mucosal blood flow was used as a validated measure of extrinsic autonomic nerve function. METHODS: Sixteen consecutive patients with SRUS (12 women; mean age 35 years) and 26 healthy controls (17 women; mean age 36 years) were studied. Laser Doppler mucosal flowmetry was performed before and after biofeedback treatment. Symptoms were documented before and after biofeedback treatment using a standardised prospectively applied questionnaire. RESULTS: Twelve of 16 patients (75%) reported subjective symptomatic improvement after treatment. Five of the 16 patients (31%) had sigmoidoscopic ulcer resolution. Pretreatment rectal mucosal blood flow was significantly lower in patients with SRUS compared with controls (163 (27) v 186 (14) flux units (FU) (mean (SD)); p<0.01). Biofeedback resulted in a significant improvement in rectal mucosal blood flow in subjects who felt subjectively better after biofeedback (p = 0.001), from 165 (30) FU to 190 (40) FU. CONCLUSION: Gut directed biofeedback is an effective behavioural treatment for the majority of patients with SRUS. Mucosal blood flow is reduced to a similar level seen in normal transit constipation, suggesting similar impaired extrinsic autonomic cholinergic nerve activity. Successful outcome following biofeedback is associated with increased rectal mucosal blood flow, suggesting that improved extrinsic innervation to the gut may be partially responsible for the response to treatment. (+info)
Review article: the management of pelvic floor disorders.
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Anorectal disorders, such as faecal incontinence, defecation difficulty and conditions associated with anorectal pain, are commonly encountered in the practices of gastroenterologists, urogynaecologists and colorectal surgeons. The evaluation of these disorders has been very much improved by the development and wider availability of diagnostic tests, such as manometry, endo-anal ultrasound, static and dynamic pelvic magnetic resonance imaging and electromyography. After briefly reviewing the normal anatomy and physiology of the anorectum, the pathophysiology and diagnostic approaches to faecal incontinence, defecation disorders and functional anorectal pain are discussed. Until recently, the management of these disorders has been largely anecdotal. However, our therapeutic armamentarium has been expanded by pharmacological agents, such as nitrates, calcium channel blockers and botulinum toxin, as well as the development of novel techniques, such as sacral nerve stimulation. These and other pharmacological, behavioural and surgical approaches are reviewed with respect to the robustness of evidence to support their efficacy in patients with these disorders. (+info)
Synaptic interactions between thalamic and cortical inputs onto cortical neurons in vivo.
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To study the interactions between thalamic and cortical inputs onto neocortical neurons, we used paired-pulse stimulation (PPS) of thalamic and cortical inputs as well as PPS of two cortical or two thalamic inputs that converged, at different time intervals, onto intracellularly recorded cortical and thalamocortical neurons in anesthetized cats. PPS of homosynaptic cortico-cortical pathways produced facilitation, depression, or no significant effects in cortical pathways, whereas cortical responses to thalamocortical inputs were mostly facilitated at both short and long intervals. By contrast, heterosynaptic interactions between either cortical and thalamic, or thalamic and cortical, inputs generally produced decreases in the peak amplitudes and depolarization area of evoked excitatory postsynaptic potentials (EPSPs), with maximal effect at approximately 10 ms and lasting from 60 to 100 ms. All neurons tested with thalamic followed by cortical stimuli showed a decrease in the apparent input resistance (R(in)), the time course of which paralleled that of decreased responses, suggesting that shunting is the factor accounting for EPSP's decrease. Only half of neurons tested with cortical followed by thalamic stimuli displayed changes in R(in). Spike shunting in the thalamus may account for those cases in which decreased synaptic responsiveness of cortical neurons was not associated with decreased R(in) because thalamocortical neurons showed decreased firing probability during cortical stimulation. These results suggest a short-lasting but strong shunting between thalamocortical and cortical inputs onto cortical neurons. (+info)
Review article: Recent trends in diagnosis and treatment of faecal incontinence.
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The inability to control bowel discharge is not only common but extremely distressing. It has a negative impact on a patient's lifestyle, leads to a loss of self-esteem, social isolation and a diminished quality of life. Faecal incontinence is often due to multiple pathogenic mechanisms and rarely due to a single factor. Normal continence to stool is maintained by the structural and functional integrity of the anorectal unit. Consequently, disruption of the normal anatomy or physiology of the anorectal unit leads to faecal incontinence. Currently, several diagnostic tests are available that can provide an insight regarding the pathophysiology of faecal incontinence and thereby guide management. The treatment of faecal incontinence includes medical, surgical or behavioural approaches. Today, by using logical approach to management, it is possible to improve symptoms and bowel function in many of these patients. (+info)
Gaze affects pointing toward remembered visual targets after a self-initiated step.
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We have investigated pointing movements toward remembered targets after an intervening self-generated body movement. We tested to what extent visual information about the environment or finger position is used in updating target position relative to the body after a step and whether gaze plays a role in the accuracy of the pointing movement. Subjects were tested in three visual conditions: complete darkness (DARK), complete darkness with visual feedback of the finger (FINGER), and with vision of a well-defined environment and with feedback of the finger (FRAME). Pointing accuracy was rather poor in the FINGER and DARK conditions, which did not provide vision of the environment. Constant pointing errors were mainly in the direction of the step and ranged from about 10 to 20 cm. Differences between binocular fixation and target position were often related to the step size and direction. At the beginning of the trial, when the target was visible, fixation was on target. After target extinction, fixation moved away from the target relative to the subject. The variability in the pointing positions appeared to be related to the variable errors in fixation, and the co-variance increases during the delay period after the step, reaching a highly significant value at the time of pointing. The significant co-variance between fixation position and pointing is not the result of a mutual dependence on the step, since we corrected for any direct contributions of the step in both signals. We conclude that the co-variance between fixation and pointing position reflects 1) a common command signal for gaze and arm movements and 2) an effect of fixation on pointing accuracy at the time of pointing. (+info)
The perceptions of force and of movement in a man without large myelinated sensory afferents below the neck.
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1. Motor memory and the sense of effort have been investigated in a man with a complete large fibre sensory neuropathy for over 16 years. The perceptions of pain, heat, cold and muscular fatigue remained but he was without perceptions of light touch and proprioception below the neck. 2. The subject was able to discriminate weights held in the hand with an accuracy only slightly worse than control subjects (20 g in 200 g) when forearm movement and visual inspection were allowed. With eyes shut however he could only distinguish a weight of 200 g from 400 g. It is concluded that a crude sense of effort remains which may have a peripheral origin. 3. A limited motor memory was also present, which allowed him to maintain a posture or continue a simple repetitive movement. No novel movement was possible without visual feedback. 4. Differences in movement ability between this subject and others with similar if less pure sensory neuropathies are ascribed to rehabilitation. (+info)
The human spinal cord interprets velocity-dependent afferent input during stepping.
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We studied the motor response to modifying the rate of application of sensory input to the human spinal cord during stepping. We measured the electromyographic (EMG), kinematic and kinetic patterns of the legs during manually assisted or unassisted stepping using body weight support on a treadmill (BWST) in eight individuals with spinal cord injury (SCI). At various treadmill speeds (0.27-1.52 m/s), we measured the EMG activity of the soleus (SOL), medial gastrocnemius (MG), tibialis anterior (TA), medial hamstrings (MH), vastus lateralis (VL), rectus femoris (RF) and iliopsoas (ILIO); the hip, knee and ankle joint angles; the amount of body weight support (BWS); and lower limb loading. The EMG amplitude and burst duration of the SOL, MG, TA, MH, VL, RF and ILIO were related to the step cycle duration during stepping using BWST. EMG mean amplitudes increased at faster treadmill speeds, and EMG burst durations shortened with decreased step cycle durations. Muscle stretch of an individual muscle could not account for the EMG amplitude modulation in response to stepping speed. The effects on the EMG amplitude and burst duration were similar in subjects with partial and no detectable supraspinal input. We propose that the human spinal cord can interpret complex step-related, velocity-dependent afferent information to contribute to the neural control of stepping. (+info)