Biomedical subjects

Z H Kiss

Publications and source records attributed to Z H Kiss.

9 recordsLinked to original sources

PubMed1999

Thalamic relay site for cold perception in humans.

The neural pathways subserving the sensation of temperature are virtually unknown. However, recent findings in the monkey suggest that the sensation of cold may be mediated by an ascending pathway relaying in the posterior part of the thalamic ventromedial nucleus (VMpo). To test this hypothesis we examined the responses of neurons to thermal stimulation of the skin and determined the perceptual effects of microstimulation in the VMpo region in awake patients undergoing functional stereotactic surgery. In 16 patients, microstimulation in the VMpo region evoked cold sensations in a circumscribed body part. Furthermore, at some of these sites thalamic neurons were found that responded to innocuous cooling of the skin area corresponding to the stimulation-evoked cold sensations. These data provide the first direct demonstration of a pathway mediating cold sensation and its location in the human thalamus.

Adult↗

PubMed1998

Phantom sensations generated by thalamic microstimulation.

Many amputees have a sense of their missing 'phantom' limb. Amputation can alter the representation of the body's surface in the cerebral cortex and thalamus, but it is unclear how these changes relate to such phantom sensations. One possibility is that, in amputees who experience phantom sensations, the region of the thalamus that originally represented the missing limb remains functional and can give rise to phantom sensations even when some thalamic 'limb' neurons begin to respond to stimulation of other body regions. Here we use microelectrode recording and microstimulation during functional stereotactic mapping of the ventrocaudal thalamus in amputees to determine both the responses of the neurons to stimulation of the skin and the perceptual effects of electrical activation of these neurons. Thalamic mapping revealed an unusually large thalamic stump representation, consistent with the findings from animal experiments. We also found that thalamic stimulation in amputees with a phantom limb could evoke phantom sensations, including pain, even in regions containing neurons responsive to tactile stimulation of the stump. These findings support the hypothesis that the thalamic representation of the amputated limb remains functional in amputees with phantoms.

Adult↗

PubMed1997

Deep brain stimulation and thalamotomy for tremor compared.

Deep brain stimulation (DBS) and thalamotomy are both capable of abolishing tremor. However, no technique is perfect and if thalamotomy proves inadequate so that tremor recurs, presumably because of suboptimal lesion location, the only option is to repeat the thalamotomy. With DBS all that has been necessary to date is to change the parameters of stimulation. Similarly with complications such as the "cerebellar" ones and paraesthesiae. If these occur after thalamotomy one can only wait and hope that they will subside and they do not always do so. With DBS, changing the parameters in the authors' patients has so far been successful in eliminating them. DBS, like thalamotomy is very effective for controlling tremor in Parkinson's disease (PD) and essential tremor (ET) and for improving dexterity in ET, but both techniques are less useful for the control of dopa dyskinesia, Parkinsonian rigidity, or impaired dexterity in PD, though DBS may be better than thalamotomy for the latter condition. On the other hand, both DBS and thalamotomy are very effective in improving dexterity in PD and ET may depend upon the fact that in PD bradykinesia is a major component, whereas in ET only the tremor is. The advantages of DBS over thalamotomy have to be weighed against the peculiar risks of DBS and of course, its cost.

Adult↗

PubMed1997

Patterns of neuronal firing in the human lateral thalamus during sleep and wakefulness.

The firing patterns of thalamic neurons in mammals undergo a dramatic change as the animal's state changes between sleep and wakefulness. During sleep the normal tonic firing of thalamic neurons changes into a slower bursting mode characterized by repetitive activation of a low-threshold calcium (Ca2+) current. The present report describes the patterns of thalamic neuronal firing during sleep and wakefulness in one human patient. Extracellular single neuron activity was recorded during functional stereotactic surgery in the thalamus of a patient with chronic pain, who was observed to fall asleep during the recording. Evolutive power spectra of the thalamic slow wave were used in place of cortical encephalography to confirm the patient's states of sleep and wakefulness. Twenty-nine sites were observed in motor and somatosensory thalamus (Vop, Vim, and Vc) that were characterized by the presence of neurons with bursting activity when the patient was asleep. Such bursting was not observed in the patient when she was awakened. At 14 of these sites we were able to discriminate the bursting activity of single units. In each case the cell stopped firing or its bursting was replaced by a tonic firing pattern when the patient was awakened. In three cases the patient began to lapse back into sleep and the neuron resumed firing in a bursting pattern once again. None of these units had a peripheral receptive field (RF), while several other units recorded in nearby regions that did not fire in a bursting pattern during sleep had kinesthetic or cutaneous RFs. Analysis of the intraburst firing pattern revealed increasing interspike intervals (ISI) for successive action potentials in a burst and that the duration of the first ISI in the burst decreased as the number of ISIs increased. This pattern is similar to that reported to occur as a result of a calcium spike. These data have confirmed for the first time that state-dependent changes in thalamic firing exist in the human and that the physiological substrates at the thalamic level that are involved in human sleep are similar to those observed in animals.

Adult↗

PubMed1996

Thalamic stimulation-evoked sensations in chronic pain patients and in nonpain (movement disorder) patients.

1. Little is known about the effect of central and peripheral nervous system injury on the processing of somatosensory information at the thalamic level in humans. The role of the human thalamic ventrocaudal nucleus (Vc) in nociception is not well understood because reports of nociceptive neuronal responses and stimulation-evoked pain are rare. In this study, we have characterized effects of microstimulation in the tactile region of Vc. Specifically, we investigated the incidence of painful sensations evoked by thalamic microstimulation in patients with and without chronic pain. 2. Data were obtained during stereotactic thalamic procedures for relief of pain or motor disorders. Patients were divided into three groups, those with 1) central poststroke pain (PSP, n = 13); 2) nonstroke pain (NSP, n = 23); and 3) movement disorders (controls, n = 24). Most (15 of 23) of the NSP patients had peripheral nerve damage. Tungsten microelectrodes were used to record neuronal responses in the thalamus and to deliver stimuli. Localization of tactile Vc was determined according to stereotactic coordinates and neuronal responses to innocuous somatic stimuli. At selected sites, microstimulation (1-s trains, 300 Hz, 0.1-0.2 ms pulses, < 100 microA) was performed and the patient was requested to describe the quality of the sensation and its peripheral location (projected field, PF). 3. Microstimulation in tactile Vc commonly evoked paresthesia-type sensations. Threshold stimulation never evoked pain in the NSP patients and evoked pain at only 2% of Vc sites in the movement disorder patients. In these latter 2 groups of patients, stimulation at > 98% of Vc sites evoked paresthesia. By contrast, in the PSP patients, 28% of Vc sites stimulated evoked painful sensations at threshold. Suprathreshold stimuli evoked painful sensations at 46% of Vc sites in the PSP patients but at only 8% of Vc sites in NSP patients and 12% of Vc sites in the movement disorder patients. 4. The thresholds to evoke paresthesia in the NSP and movement disorder patients were significantly lower than the thresholds in the PSP patients. However, stimulation thresholds to elicit pain were similar in all patient groups. 5. All patients were capable of differentiating stimulation-evoked paresthesia from pain. Stimulation-evoked painful sensations in the PSP patients were often described as burning and sometimes as "sharp," "shocking," or "unpleasant." By contrast, the quality of pain evoked in the other patient groups was typically described as unpleasant or shocking. Pain could be evoked at sites throughout tactile Vc, although most sites were located in the ventral 2/3 of the nucleus. 6. In the movement disorder patients, the location of the projected sensation usually corresponded to the location of the receptive fields of the tactile neurons recorded at the same site. By contrast, in both groups of pain patients there was a high incidence of mismatches between the projected and receptive fields. 7. These results suggest that the effective thalamic output from Vc to the cortex is affected by somatosensory deafferentation in pain patients. In addition, in the PSP patients there are also changes in the thalamocortical processing of noxious information. The increased incidence of thalamic-evoked pain in PSP patients may be due to 1) loss of low-threshold mechanoreceptive thalamic neurons such that nociceptive neuronal output is now prominent, 2) reduced tonic inhibition of thalamic or cortical nociceptive neurons, and/or 3) unmasking or strengthening of nociceptive pathways.

Cerebrovascular Disorders↗

PubMed1995

Visceral pain evoked by thalamic microstimulation in humans.

Microstimulation within and below the ventrocaudal nucleus (Vc) in the human thalamus typically evokes non-painful, paraesthetic cutaneous sensations. We now describe cases in which thalamic microstimulation evoked visceral pains. Data were obtained during stereotactic thalamotomy procedures. Patient 211 had a history of essential tremor. At a site 0.5 mm ventroposterior to Vc, microstimulation elicited pain described as 'deep, internal, in a straight line like my appendix pain years ago'. Patient 153 had a history of post-stroke hemibody pain. In each of two trajectories, at sites approximately 2 mm ventroposterior to Vc, microstimulation evoked pain in the groin. At one of these sites, the pain was described as 'like having a baby'. These and additional observations suggest that stimulation ventroposterior to Vc can evoke visceral pain and may trigger pain 'memories'.

Adult↗

PubMed1995

Sleeping cells in the human thalamus.

Neurons in the lateral thalamus of a patient undergoing stereotactic surgery were found to fire in a characteristic bursting pattern only when the patient was asleep. These novel observations are consistent with animal studies in which the tonic firing pattern of thalamic neurons during wakefulness changes to a bursting pattern during slow-wave sleep.

Adult↗

PubMed1995

The role of the thalamus in functional neurosurgery.

The human thalamus has been the focus of much interest as a target organ for the stereotactic surgical modification of particularly pain and movement disorders. The sites receiving the greatest attention are portions of Vc, Vim, Vop, and the medial thalamus. As such procedures require physiologic corroboration of target site, a considerable literature has arisen concerned with electrical stimulation and microelectrode recordings within them. Not only do the physiologic observations accomplish the desired localization, but they also allow an insight into normal and pathologic thalamic physiology. Yet vast areas of the thalamus remain unstudied enigmas.

Brain Mapping↗

PubMed1994

Plasticity in human somatosensory thalamus as a result of deafferentation.

Experimental studies indicate that deafferentation results in reorganization of the somatosensory map at various levels of the CNS, such that the representation of a body part adjacent to a region that is denervated expands into the deafferented area. Recent data suggest that in the human this occurs at the cortical level, but subcortical structures have not been systematically investigated. To test the hypothesis that the human thalamus is capable of significant reorganization as a result of changes in afferent input, microelectrode recording and stimulating techniques were used to define thalamic somatotopy in 61 patients undergoing stereotactic procedures. Five groups were compared: those with pain in the deafferented body part, face (n = 9), arm/hand (n = 4), leg/foot (n = 8) and hemibody (n = 5) and those with neither pain nor deafferentation, i.e., movement disorder (n = 24). Trunk representation, as determined from receptive fields, was significantly larger in patients with leg/foot deafferentation than in patients without deafferentation (1.8 +/- 0.7 vs. 0.5 +/- 0.2 mm; p < 0.01). Also, microstimulation induced paraesthesiae in the face from a significantly larger region of thalamus in the facially denervated group compared to the movement disorder group (13.8 +/- 2.8 vs. 3.7 +/- 0.6 mm; p < 0.001). There were no significant differences in the representation of other body parts in the five groups. The results in the leg-deafferented group agree with conclusions reached from animal studies; however, the human situation is more complex. There appear to be different patterns and degrees of somatotopic reorganization in the human, all of which may be associated with pain syndromes.

Afferent Pathways↗