Tactile functions after cerebral hemispherectomy.

Patients that were hemispherectomized due to brain lesions early in life sometimes have remarkably well-preserved tactile functions on their paretic body half. This has been attributed to developmental neuroplasticity. However, the tactile examinations generally have been fairly crude, and subtle deficits may not have been revealed. We investigated monofilament detection and three types of tactile directional sensibility in four hemispherectomized patients and six healthy controls. Patients were examined bilaterally on the face, forearm and lower leg. Normal subjects were examined unilaterally. Following each test of directional sensibility, subjects were asked to rate the intensity of the stimulation. On the nonparetic side, results were almost always in the normal range. On the paretic side, the patients' capacity for monofilament detection was less impaired than their directional sensibility. Despite the disturbed directional sensibility on their paretic side the patients rated tactile sensations evoked by the stimuli, on both their paretic and nonparetic body halves, as more intense than normals. Thus, mechanisms of plasticity seem adequate for tactile detection and intensity coding but not for more complex tactile functions such as directional sensibility. The reason for the high vulnerability of tactile directional sensibility may be that it depends on spatially and temporally precise afferent information processed in a distributed cortical network.

Unmyelinated tactile afferents signal touch and project to insular cortex.

There is dual tactile innervation of the human hairy skin: in addition to fast-conducting myelinated afferent fibers, there is a system of slow-conducting unmyelinated (C) afferents that respond to light touch. In a unique patient lacking large myelinated afferents, we found that activation of C tactile (CT) afferents produced a faint sensation of pleasant touch. Functional magnetic resonance imaging (fMRI) analysis during CT stimulation showed activation of the insular region, but not of somatosensory areas S1 and S2. These findings identify CT as a system for limbic touch that may underlie emotional, hormonal and affiliative responses to caress-like, skin-to-skin contact between individuals.

Directional sensibility of hairy skin and postural control.

People can feel and report the direction of very small movements which cause changes in the tension of the forearm's hairy skin. This subjective sensory function may perhaps reflect more fundamental sensorimotor tasks. The hypothesis was investigated by measuring body sway and movement of six female and male volunteers who were performing the tandem-stance Romberg test with open and closed eyes. The increase in sway and movement after eye closure was reduced significantly when the subjects were allowed to use one forearm to touch a spatially fixed object from below. Three objects were used, a solid Perspex rod, an easily rotating steel ball, and a pointed metal peg whose tip was attached to the skin with a droplet of contact glue. Possible mechanical support could be excluded on basis of the objects' technical properties and the magnitudes of forearm movements. Movement of the forearm relative to an object could provide spatial information about changes of the forearm's position in space. Likewise, changes of skin tension that were caused by such movements could be useful. The Perspex rod and the steel ball might provide both types of information. However, the glued peg only caused changes of skin tension, but reduced sway and movement equally effectively. Therefore, information from tension receptors of the forearm's hairy skin underlying the accurate subjective directional sensibility also appears to participate in basic motor control.

Stimulus pattern and tolerance development. Exposure of rats to alternating light/darkness patterns in vivo and pilocarpine sensitivity in vitro of the iris sphincter.

Pigmented rats were kept under different light/darkness patterns for 5-12 days. The response of the iris sphincter in enucleated eyes was tested with pilocarpine as a standard stimulus. The eyes were either decorneated or intact. The maximum response (no subsensitivity) was obtained after continuous darkness and the minimum (maximum subsensitivity) after continuous light. Six hours of light and one block of 18 hours of darkness per day caused distinct subsensitivity, but less than if the light was interrupted by six 3-hour darkness periods. Further subdivision of the light into twelve 30-min. periods made no difference. One 18-hour block of light followed by 6 hours of darkness caused less subsensitivity than continuous light. Subdividing the darkness into six 1-hour periods made no significant difference.

Anticoagulant vs anti-platelet therapy as prophylactic against cerebral infarction in transient ischemic attacks.

156 patients with transient ischemic attacks (TIA) or reversible ischemic neurological deficit (RIND) were given prophylactic anticoagulant (AC) treatment against cerebral infarction in a prospective multicenter study from 5 hospitals in southern Sweden. After 2 months of AC treatment, 135 patients remained in the study and were randomized into 2 groups; one continued with AC treatment and one changed to anti-platelet therapy. The patients were followed for 12 months. No significant difference was seen between the 2 groups but 3 completed cerebral infarctions occurred during anti-platelet therapy against one during AC treatment. One cerebral hemorrhage was seen during AC treatment. All completed strokes occurred in men who initially had carotid symptoms. The number of patients with TIA/RIND was somewhat higher in the anti-platelet group whereas myocardial infarctions occurred more often during AC treatment. Compared to the natural history of untreated TIA/RIND both treatments were found to have a prophylactic effect against cerebral infarction.