PubMed Health⌕ Search

Biomedical subjects

F A Lenz

Publications and source records attributed to F A Lenz.

At least 73 records · Page 4Linked to original sources
PubMed1996

Evidence that excitatory amino acids mediate afferent input to the primate somatosensory thalamus.

Neurons in and posterior to the primate sensory nucleus of the thalamus (VPL) were tested for excitation by iontophoretically applied excitatory amino acid agonists. In addition, in several cells the effects of iontophoretically applied excitatory amino acid antagonists on the responses to cutaneous stimuli were examined. All neurons showed responses to all agonists. The responses of several neurons to cutaneous stimuli were attenuated or blocked by local administration of receptor antagonists. These results provide initial evidence that somatosensory responses of neurons in the primate thalamus are mediated by excitatory amino acids.

Afferent Pathways↗
PubMed1995

Statistical prediction of the optimal site for thalamotomy in parkinsonian tremor.

Stereotactic lesions in the thalamus for treatment of parkinsonian tremor are often made at the location where neurons fire at approximately tremor frequency (tremor cells). Some of these cells show a large amount of activity at tremor frequency and are significantly correlated with electromyographic activity (EMG) during tremor. Our analysis of cellular location identifies a cluster of neurons showing activity characterized both by concentration of power at tremor frequency and by significant correlation with EMG. In a retrospective analysis of results in 15 patients, lesions placed within 2 mm of the center of this cluster were uniformly effective in relieving tremor. Therefore, a small lesion targeting this cluster is effective in treatment of parkinsonian tremor.

Brain Mapping↗
PubMed1995

Stimulation in the human somatosensory thalamus can reproduce both the affective and sensory dimensions of previously experienced pain.

Thalamic structures involved in the unpleasant emotional or affective aspect of pain are poorly understood. We now describe studies of the region of the thalamic principal somatosensory nucleus (Vc) performed before thalamotomy for tremor in a patient who also had panic disorder. Microstimulation in the region posterior to Vc evoked chest pain, including a strong affective dimension, almost identical to that occurring during his panic attacks, as measured using a questionnaire. Results in our other patients indicate that stimulation-associated pain with a strong affective dimension occurred only in those patients who had previously experienced spontaneous pain with a strong affective component. These results are consistent with stimulation-evoked activation of limbic structures, which are connected through cortex with the region posterior to Vc and involved in the affective dimension of pain through conditioning by previous experience.

Adult↗
PubMed1994

A population of cells in the human thalamic principal sensory nucleus respond to painful mechanical stimuli.

A population of neurons located in the cutaneous core of the principal sensory nucleus of human thalamus (ventralis caudalis, Vc) has been identified that had their maximal response to mechanical stimuli which were perceived as painful by the patients involved. None of these cells responded to painful thermal stimuli. The graded responses of these cells to mechanical stimuli extending into the painful range suggest they both mediate acute pain in response to mechanical stimuli and participate in mechanical hyperalgesia.

Electric Stimulation↗
PubMed1994

Single unit analysis of the human ventral thalamic nuclear group. Tremor-related activity in functionally identified cells.

During procedures for parkinsonian tremor, neurons in the thalamic ventral nuclear group show periodic activity at tremor frequency (tremor-frequency activity). The tremor-frequency activity of some cells is significantly correlated with tremor. Cells in this region also display functional properties defined by activity related to somatosensory stimuli and to active movement. Cells with activity related to somatosensory stimulation were termed sensory cells while those with activity related to active movement were termed voluntary cells. Cells with activity related to both somatosensory stimulation and active movement were termed combined cells. Those with activity related to neither somatosensory stimulation nor active movement were termed no-response cells. Combined, voluntary and no-response cells were located in the region of thalamus where a lesion stops tremor and anterior to the region where sensory cells were found. Spectral cross-correlation analysis demonstrated that many combined, voluntary and no-response cells had a peak of activity at tremor frequency which was significantly correlated with electromyogram (EMG). Analysis of the phase of thalamic activity relative to EMG activity indicated that voluntary and combined cell activity usually led EMG during tremor. These results suggest that thalamic cells unresponsive to somatosensory stimulation (voluntary and no-response cells) and those responsive to somatosensory stimulation (combined cells) are involved in the mechanism of parkinsonian tremor. The activity of sensory cells frequently lagged behind tremor while activity of combined cells often led tremor. This finding suggests that the activity of these two cell types, both responding to sensory input, is related to tremor by different mechanisms.

Electromyography↗
PubMed1994

Characteristics of somatotopic organization and spontaneous neuronal activity in the region of the thalamic principal sensory nucleus in patients with spinal cord transection.

1. We explored the region of the principal sensory nucleus of thalamus (Vc) during stereotactic surgical procedures for treatment of patients with pain after spinal cord transection (n = 23). Receptive fields (RFs) of thalamic single neurons and locations of sensations evoked by stimulation (projected field, PF) were determined by standard methods. The cellular thalamic region where sensations were evoked at < 25 microA was termed the "region of Vc." The region of Vc in spinal patients was subdivided into different areas according to RF and PF locations. Areas that were distant from the representation of the anesthetic part of the body were termed "spinal control" areas, whereas those that were adjacent to or included in the representation of the area of absolute sensory loss were termed "border zone/anesthetic" areas. The region of Vc in movement disorder patients were termed the "control" area. 2. Border zone/anesthetic areas of thalamus often exhibited increased representations of the border of the anesthetic part of the body in comparison with the representation of the same parts of the body in control and spinal control areas. 3. In control and spinal control areas the locations of RFs and PFs were usually well matched. However, in border zone/anesthetic areas of the thalamus there was frequently a mismatch between the location of RFs and PFs (RF/PF mismatch). In border zone/anesthetic areas, RFs were often located on the border of the anesthetic part of the body whereas PFs were referred to anesthetic parts of the body. 4. Analysis of first- and higher-order properties of spontaneous neuronal activity revealed that spike trains could be classified into two groups with distinct patterns of activity. The R group (n = 49) was characterized by independence of sequential interspike intervals (ISIs), a Poisson distribution of ISIs, initially inhibitory or flat autocovariance function (acvf), and low level of high-frequency bursting. The O group (n = 26) was characterized by correlation of sequential ISIs, large sustained postspike facilitation on the acvf, and high prevalence of high-frequency bursting--all consistent with a bursting pattern of activity. A third group of spike trains (n = 17) had an initially inhibitory or flat acvf and a unimodal, positively shifted, ISI distribution that did not meet criteria for a Poisson distribution. 5. Spike trains in the R group were much more common in control and control spinal areas, whereas those in the O group were more common in border zone/anesthetic areas.(ABSTRACT TRUNCATED AT 400 WORDS)

Brain Mapping↗
PubMed1994

Distribution and response evoked by microstimulation of thalamus nuclei in patients with dystonia and tremor.

The effect of 806 microstimulations were observed in 16 patients with movement disorders, dystonia (DA, n = 6) and tremor (TR, n = 10). Among the 347 sites in DA patients motor response was seen at 29 sites, the response with increased dystonia was seen at 28 sites. The effect could be seen at 14 sites (50%) in ventrointermedialis (Vim), five sites (18%) in ventrocaudalis (Vc) and five sites (18%) in white matter (Wm). As for the other four sites, one site was in ventraloralis anterior (Voa), two sites in ventraloralis posterior (Vop), and one site in dorsal thalamus (dth), but reduction of dystonia drive was only seen at one site in dth. On the other hand, among the 459 sites in TR patients, motor response leading to reduction of tremor drive was seen at 38 sites, of which 30 sites (79%) were noted in Vim nuclei, and five sites (13.2%) in vc nuclei; of the remaining sites, two were seen in Vop nuclei, one in dth, and no increasing tremor drive was observed in all area. In general, paresthesia was the most common response, which was found at 159 sites (45.8%) with DA and 216 sites (47.1%) with TR. Pain was only seen at one site in Wm of DA; warm/cold and vertigo could be seen in Vop, Vim, and vc nucleus respectively. No responses were shown at 156 sites (45%) in DA, and 201 sites (43.8%) in TR.

Dystonia↗
PubMed1993

Neurons in the area of human thalamic nucleus ventralis caudalis respond to painful heat stimuli.

A population of neurons in the area of human thalamic nucleus ventralis caudalis (Vc) respond to noxious heat stimuli. In the cutaneous core of Vc 6% (6/108) of recorded neurons had a significantly greater response to noxious heat stimuli than to innocuous control stimuli. Half of these neurons (n = 3) also responded to innocuous cold stimuli. Within the region posterior and inferior to the cutaneous core of Vc 5% (4/77) of neurons responded exclusively to noxious heat stimuli. Cells responding to noxious heat were recorded at a greater proportion (66%) of sites where painful sensations were evoked by microstimulation than at sites where nonpainful sensations were evoked (1.5%). The results suggest that neurons in the region of human Vc mediate the sensory aspect of pain.

Electric Stimulation↗
PubMed1993

Thermal and pain sensations evoked by microstimulation in the area of human ventrocaudal nucleus.

1. We have studied the sensations evoked by threshold microstimulation (TMS) in the area of the human principal sensory nucleus of the thalamus [ventralis caudalis (Vc)] in patients (n = 11) undergoing stereotactic surgery for the treatment of movement disorders and pain. Preoperatively, patients were trained to describe somatic sensory stimuli using a standard list of descriptors. This same list was used to describe sensations evoked intraoperatively by thalamic microstimulation. Stimulation sites (n = 216) were defined by location within the area where the majority of cells had a reproducible response to innocuous cutaneous stimulation (core region) or in the cellular area posterior and inferior to the core region (posteroinferior region). 2. TMS-evoked sensations were categorized as paresthetic if the descriptors "tingle," "vibration," or "electric current" were chosen by the patient to describe the sensation and as thermal/pain if the descriptors "cool," "warm," "warm and cool," or "pain" were chosen. Thermal/pain sensations were evoked by stimulation in 82% (9/11) of patients and at 19% of sites studied. These results suggest that thalamic microstimulation can evoke thermal/pain sensations reproducibly across patients. 3. Thermal/pain sensations were evoked more frequently by stimulation at sites in the posteroinferior region (30%) than by stimulation at sites in the core region (5%). Nonpainful thermal sensations composed the majority of thermal/pain sensations evoked by stimulation in both the core (80%) and posteroinferior regions (86%). Sites where stimulation evoked pain and nonpainful cool sensations were found anterior to the area where nonpainful warm sensations were evoked. Thermal/pain sensations were evoked at sites located medially near the border between the core and posteroinferior regions. 4. Radiologic techniques were used to determine the presumed nuclear location of stimulation sites. Thermal/pain sensations were evoked less frequently by stimulation in the part of Vc included in the core region than by stimulation in any of the following: the part of Vc included in the posteroinferior region, ventralis caudalis portae nucleus, ventralis caudalis parvocellularis nucleus, or the white matter underlying the ventral nuclear group. 5. The location of the sensation evoked by stimulation [projected field (PF)] varied widely in size. PFs were categorized as large if they involved more than one part of the body (e.g., face and arm) or if they crossed at least one joint proximal to the metacarpophalangeal joint or to the metatarsophalangeal joint. PFs were more frequently large at sites where thermal/pain sensations were evoked by TMS (33%) than at those where paresthesia were evoked (6%).(ABSTRACT TRUNCATED AT 400 WORDS)

Brain Mapping↗
PubMed1993

Role of the thalamus in parkinsonian tremor: evidence from studies in patients and primate models.

The electrophysiologic basis of parkinsonian tremor is discussed in terms of the central oscillator and peripheral feedback hypotheses of tremor. Recent studies in monkeys and humans suggest that parkinsonian tremor may result from the activity of a central oscillator, possibly located in the basal ganglia. Peripheral somatosensory input seems to modulate tremor and central nervous system activity related to tremor.

Animals↗
PubMed1993

Effective response evoked by microstimulation of thalamus nuclei in patients with tremor.

459 microstimulations were done in 10 patients with tremor. The motor evoked response with reduction tremor drive was observed at 38 sites, of which 30 (79%) were noted in ventrointermedialis (vim) nuclei, and 5 (13.2%) in ventrocaudalis (vc) nuclei, 2 in ventroralis posterior (vop) nuclei, 1 in dorsal thalamus (dth). No increased tremor drive response was noted in all the sites. Paresthesia was the most common response (47.1%). Except pain at 1 site in vc nuclei, warm/cold and vertigo were noted in vop, vim, vc nuclei. No responses accounted for 43.8%.

Electric Stimulation↗
PubMed1990

Single unit analysis of the human ventral thalamic nuclear group. Activity correlated with movement.

During neurosurgical operations for the relief of movement disorders, single thalamic neurons (n = 107) were identified with activity which was related to verbally cued active movements (movement-related cells). The activity of each neuron was examined during different contralateral movements in order to determine the movement which was associated with the most consistent and pronounced change in firing rate (the optimal response). The optimal response was determined by analysis of histograms of neuronal activity which were constructed by using the onset of EMG activity to synchronize successive repetitions of the active movement. Movement-related cells exhibited optimal responses associated with such movements as making a fist, extension or flexion of the wrist, flexing or extending the elbow, pointing with the entire upper extremity, extending the tongue and lifting the leg. Most movement-related cells recorded in a single parasagittal plane in an individual patient had optimal responses related to movements involving the same part of the body. Movement-related cells were classified into those that were activated in response to somatosensory stimulation (combined cells, n = 20) and those which were not (voluntary cells, n = 87). Combined cells were activated in advance of EMG activity during active movement and so could be distinguished from cells responding only to sensory stimulation (sensory cells). Movement-related cells (combined and voluntary cell types) were located anterior to sensory cells and tended to show a mediolateral somatotopic organization parallel to that of sensory cells with cutaneous receptive fields. Combined cells responded to somatosensory stimulation of the same part of the body as that involved in the active movement related to the optimal response of the cell. Combined cells responding to passive movements of a joint always had their optimal response during active movement about the same joint. The activity of combined cells during parkinsonian tremor may clarify the role of sensory feedback in tremor.

Electric Stimulation↗
PubMed1990

Thalamic single-unit activity occurring in patients with hemidystonia.

Lesions of the ventrolateral complex of the human thalamus may relieve abnormal movements in patients with dystonia. We have now recorded the thalamic single-unit activity and the electromyographic (EMG) activity in the upper extremity during the physiologic localization which is required prior to thalamotomy for hemidystonia. The activity of thalamic single units was correlated with the EMG signal by spectral methods. Results of this analysis indicate that a group of thalamic cells show a concentration of activity, occurring at the same frequency as the EMG activity during dystonia. In many cases, there was statistically significant correlation between thalamic and EMG signals at the frequency of dystonia. The activity of these cells may be involved in the generation of dystonic movements.

Dominance, Cerebral↗
PubMed1989

Characteristics of the bursting pattern of action potentials that occurs in the thalamus of patients with central pain.

Neurons in the somatosensory thalamus of patients with central pain following spinal cord injury fire in bursts of action potentials more frequently than do similar neurons in patients without pain. Furthermore, the characteristic firing pattern within these bursts is similar to that which is shown to be associated with the occurrence of calcium spikes in intracellular studies of thalamic nuclei. This finding may have significant implications for the etiology and treatment of central pain states.

Action Potentials↗
PubMed1989

Detection of feedback in the central nervous system using system identification techniques.

An analysis method to detect the presence of feedback between biological signals, particularly those associated with the central nervous system, is presented. The technique is based on recent results in the system identification literature involving the concept of a feedback free process. It may be applied to volume conducted signals such as EEG and EMG, as well as to neuronal spike trains through the use of a data transformation procedure. The utility of the technique is then demonstrated in a study of the relationship between Parkinsonian tremor and certain tremor cells found in the thalamus of Parkinsonian patients, using data collected during thalamotomies. The results obtained suggest that feedback mechanisms may be an important factor contributing to Parkinsonian tremor.

Biofeedback, Psychology↗
PubMed1989

Recordings of abnormal activity in patients with deafferentation and central pain.

We have performed a single-unit analysis of the spontaneous activity of cells in 9 patients with central and deafferentation pain and 4 patients without pain. These studies have concentrated on the analysis of cells firing in bursts, which are particularly prevalent in pain patients. These cells were found to fire typically at interspike intervals of 1-2 ms and interburst intervals of 50 ms. Such cells occurred throughout nucleus ventralis caudalis, nucleus ventrocaudalis parvocellularis and possibly nucleus ventralis intermedius and are different in terms of firing characteristics and locations from bursting cells found in non-pain patients.

Afferent Pathways↗
PubMed1989

Thalamic stimulation and recording in patients with deafferentation and central pain.

Thalamic exploration was carried out in 39 patients with central or deafferentation pain. Several patients were explored more than once or bilaterally; therefore, 52 explorations were carried out. In 16 cases, microelectrode recording and microstimulation were employed. In the deafferented thalamus, a phenomenon of central allodynia was identified, in which patients with hyperpathia experience pain on stimulation rather than the usual sensations. With microrecording, a distinct unit firing in bursts can be identified and classified into three types. In several patients, the thalamic somatotopic map is found to be altered, and this reorganization can be classified into four types.

Afferent Pathways↗