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F A Lenz

Publications and source records attributed to F A Lenz.

82 records · Page 5Linked to original sources
PubMed1988

Single-unit analysis of the human ventral thalamic nuclear group: somatosensory responses.

1. We have studied the functional and somatotopic properties of 531 single mechanoreceptive thalamic neurons in humans undergoing stereotactic surgery for the control of movement disorders and pain. The majority of these somatosensory cells had small receptive fields (RFs) and were activated in a reproducible manner by mechanical stimuli applied to the skin or deep tissues. These neurons, which we termed "lemniscal," could be further classified into those responding to stimulation of cutaneous (76% of lemniscal sensory cells) or deep (24%) structures. 2. The incidence of neurons having cutaneous or mucosal RFs in the perioral region, thumb, and fingers (66%) was much higher than that of neurons having RFs elsewhere on the body. Most of the deep cells were activated by movements of and/or mechanical stimuli delivered to muscles or tendons controlling the elbow, wrist, and fingers. 3. Sequences of cells spanning several millimeters in the parasagittal plane often exhibited overlapping RFs. However, RFs changed markedly for cells separated by the same distances in the mediolateral direction. This suggests that the cutaneous somatotopic representation of each region of the body is organized into relatively thin sheets of cells oriented in the parasagittal plane. 4. By comparing neuronal RFs in different parasagittal planes in thalamus of individual patients we have identified a mediolateral representation of body surface following the sequence from: intraoral structures, face, thumb through fifth finger to palm, with forearm and leg laterally. 5. Along many trajectories in the parasagittal plane the sequence of cells with overlapping RFs was interrupted by another sequence of cells with RFs corresponding to a different body region. The RFs of the intervening sequence characteristically represented body regions known to be located more medially in thalamus (see 3 above). These findings could be explained if the lamellae postulated above were laterally convex. 6. Cells responding to deep stimulation (deep cells) could be further classified into those responding to joint movement (63%), deep pressure (15%), or both (22%). Deep cells were found usually at the anterior-dorsal border and sometimes at the posterior border of the region containing cells responding to cutaneous stimuli. Although there was some overlap in the RFs, deep cells representing wrist were found medial to those representing elbow, and both of these were found medial to cells representing leg.(ABSTRACT TRUNCATED AT 400 WORDS)

Brain Mapping↗
PubMed1988

Methods for microstimulation and recording of single neurons and evoked potentials in the human central nervous system.

An apparatus and technique are described for microstimulation and recording of both slow wave and single neuron (single unit) activities during functional stereotaxic procedures. This method facilitates microstimulation and evoked potential and single unit analysis which, in combination, provide optimum definition of stereotaxic targets in the treatment of functional disorders of the human central nervous system.

Brain↗
PubMed1988

Single unit analysis of the human ventral thalamic nuclear group: correlation of thalamic "tremor cells" with the 3-6 Hz component of parkinsonian tremor.

Although cells firing at tremor frequency, called "tremor cells" (Guiot et al., 1962), have often been recorded in the thalamus of parkinsonian patients, the extent of correlation between these spike trains and tremor has rarely been assessed quantitatively. This paper describes spectral cross-correlation functions calculated between the activity of "tremor cells" and electromyogram (EMG) signals recorded from several muscles in the contralateral arm. The power occurring in the spike train at tremor frequency was described in absolute terms by the spike autopower, and in relation to the average for all spectral components by the spike autopower signal-to-noise ratio (spike autopower SNR). The probability of significant cross-correlation between the thalamic spike train and EMG at tremor frequency was assessed by the coherence at tremor frequency. Autopower spectra of the activity of many of these cells exhibited a concentration of power at tremor frequency, indicated by spike autopower SNRs as high as 18. Of the EMG signals studied, signals recorded from finger flexors were most often significantly correlated at tremor frequency. Significant correlation between the thalamic spike train and finger flexor EMG activity was found in 34% of cells analyzed. Tremor frequency coherence was significantly correlated with tremor frequency spike autopower (r = 0.46, p less than 0.0001) and spike autopower SNR (r = 0.533, p less than 0.0001). The proportion of cells with a spike autopower SNR greater than 2 that were significantly correlated with finger flexor EMG activity was greater than that of cells with a spike autopower SNR of less than 2 (p less than 0.001; chi-square). Therefore, cells exhibiting a large amount of power at tremor frequency were those best correlated with EMG activity during tremor. Some of these cells may be involved in the generation of tremor.

Action Potentials↗
PubMed1987

Long-latency reflex activity in squirrel monkeys with occlusion of the middle cerebral artery.

The primate middle cerebral artery (MCA) preparation has been studied as an animal model of human spasticity resulting from stroke. MCA occlusion in 3 squirrel monkeys was accomplished through a transorbital approach and animals were evaluated by 'clinical' examinations and studies of EMG responses to torque motor imposed joint displacement. Animals were transiently hemiparetic but not spastic postoperatively, although all were found to have a large infarct in MCA territory on post-mortem examination. The electromyographic (EMG) response of biceps in normal animals to torque motor imposed elbow extension consisted of both early (M1) and late (M2) components (Tatton et al. 1975). These components were unchanged following MCA occlusion. The EMG response to metacarpophalangeal joint extension in finger flexors or normal animals consisted solely of a long-latency (M2) component (Lenz et al. 1983a). Following MCA occlusion the M2 component in this muscle was decreased or absent, but a short-latency (M1) component appeared.

Animals↗
PubMed1987

Selection of the optimal lesion site for the relief of parkinsonian tremor on the basis of spectral analysis of neuronal firing patterns.

Techniques for quantitatively describing the firing properties of neurons have been used to identify thalamic cells with a firing pattern which is correlated with EMG activity during tremor. By locating these cells relative to the anterior border of the somatosensory nucleus and the anterior commissure-posterior commissure line, it may be possible to select the optimal lesion site for the relief of parkinsonian tremor on a rational rather than an empirical basis.

Humans↗
PubMed1987

Thalamic microelectrode recording and microstimulation in central and deafferentation pain.

Microelectrode recording and microstimulation (in 1 case macrostimulation) were used to localize stereotactic targets in 8 patients with central and deafferentation pain and 1 'deafferented control' patient without pain. Off-line study revealed two features commonly proposed as potential physiological factors for such pain, but they were present in both pain and control patients--somatotopographic reorganization and the presence of bursting cells. In all patients in whom stimulation induced pain referred to deafferented parts of the contralateral body, hyperpathia or allodynia were present instead of normal paraesthetic, sensorimotor or thermal responses.

Electric Stimulation↗
PubMed1985

Cross-correlation analysis of thalamic neurons and EMG activity in parkinsonian tremor.

Bursting activity in cells cross-correlated with electromyographic (EMG) activity during parkinsonian tremor. Statistically significant evidence of cross-correlation was found for 49% of cells located at the lesion target for relief of tremor. Statistically significant correlation was found for 90% of cells having tremor frequency power greater than twice 'average power' at nontremor frequencies. This population of cells may be involved in the generation of parkinsonian tremor.

Electromyography↗
PubMed1983

Electromyographic response to displacement of different forelimb joints in the squirrel monkey.

The electromyographic (EMG) reflex response evoked in muscles stretched by imposed angular joint displacement has previously been studied in a variety of muscles and species. In most muscles studied, the EMG response consists of an initial burst of activity at latencies comparable to tendon tap responses followed by one or more bursts of EMG activity occurring at latencies less than somatosensory reaction time. The longer latency bursts or peaks of activity have often been assumed to be of similar origin in functionally diverse muscles. The present experiments were performed to examine the EMG response to imposed joint displacement in several different muscles of the squirrel monkey forelimb. The EMG was studied in muscles stretched by elbow, wrist, and metacarpophalangeal joint extension. Early (M1) and long (M2) latency peaks of activity could be observed in the EMG responses of short head of biceps (SHB), flexor carpi ulnaris (FCU), and flexor digitorum profundus (FDP), at latencies which are similar to those reported in other primate species allowing for differences in the size of the animals. The intervals between these peaks did not correspond to the period of oscillations in tension which occurred after the onset of the joint extension. The M2 peak consistently occurred later in SHB than in FCU and FDP. The M1 peak was smaller in distal than in proximal muscles and was frequently absent in FDP at resting levels of EMG activity. The ratio of M1 to M1 + M2 activity for different muscles revealed that proximal muscles had prominent early with less prominent long latency activity, whereas distal muscles had minimal early latency activity with prominent long latency activity. The onset of EMG activity approached tendon tap latencies in FCU at high base line EMG levels but in most cases occurred at approximately twice tendon tap latencies in FDP at high base line EMG levels. The results demonstrate the presence of significant differences between the EMG response to joint displacement in the proximal-distal series of forelimb flexors. Differences in the reflex response to joint displacement are discussed in view of twitch times and motor unit composition of the muscles studied.

Animals↗
PubMed1983

The effect of cortical lesions on the electromyographic response to joint displacement in the squirrel monkey forelimb.

The extent of participation of supraspinal structures in the generation of the long latency (M2) electromyographic (EMG) response to imposed joint displacement may be reflected in the effect of lesions of the central nervous system. M2 activity has been reported in a variety of studies to be either present or absent following supraspinal lesions. Since other studies have shown different characteristics of long latency activity in proximal as compared to distal upper limb muscles in primates, the present experiments were conducted to determine the effect of motor cortical (area 4) lesions on reflex activity generated in a proximal versus a distal upper limb muscle. Chronic experiments were performed on squirrel monkeys with unilateral lesions of the forelimb motor cortex (area 4) which was mapped with the aid of electrical stimulation. Input-output relationships were determined between torque motor-imposed joint rotation and the EMG response in the stretched muscles (flexor digitorum profundus (FDP) and short head of biceps (SHB)). The EMG responses were reported as a percentage of maximum EMG output and controlled for base line EMG level. The "gain" (slope of EMG response versus torque load) for FDP M2 activity was markedly decreased in the limb contralateral to the area 4 lesion as compared to the opposite limb. This decrease was independent of base line EMG levels. In SHB, early latency (M1) EMG activity was significantly increased, but M2 activity appeared unaffected on the side contralateral to the lesion. The results demonstrate that the central and peripheral mechanisms generating M2 activity in FDP differ from those in SHB in terms of motor cortical dependency.

Animals↗