Frederick A. Lenz

Bio: Frederick A. Lenz is an academic researcher from Johns Hopkins University. The author has contributed to research in topics: Thalamus & Somatosensory system. The author has an hindex of 47, co-authored 178 publications receiving 8002 citations. Previous affiliations of Frederick A. Lenz include Johns Hopkins University School of Medicine & Toronto General Hospital.

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

Abstract: 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.

Cortical representation of pain: functional characterization of nociceptive areas near the lateral sulcus

Abstract: Many lines of evidence implicate the somatosensory areas near the lateral sulcus (Sylvian fissure) in the cortical representation of pain. Anatomical tracing studies in the monkey show nociceptive projection pathways to the vicinity of the secondary somatosensory cortex in the parietal operculum, and to anterior parts of insular cortex deep inside the Sylvian fissure. Clinical observations demonstrate alterations in pain sensation following lesions in these two areas in human parasylvian cortex. Imaging studies in humans reveal increased blood flow in parasylvian cortex, both contralaterally and ipsilaterally, in response to painful stimuli. Painful stimuli (such as laser radiant heat) evoke potentials with a scalp maximum at anterior temporal positions (T3 and T4). Several dipole source analyses as well as subdural recordings have confirmed that the earliest evoked potential following painful laser stimulation of the skin derives from sources in the parietal operculum. Thus, imaging and electrophysiological studies in humans suggest that parasylvian cortex is activated by painful stimuli, and is one of the first cortical relay stations in the central processing of these stimuli. There is mounting evidence for closely located but separate representations of pain (deep parietal operculum and anterior insula) and touch (secondary somatosensory cortex and posterior insula) in parasylvian cortex. This anatomical separation may be one of the reasons why single unit recordings of nociceptive neurons are scarce within regions comprising low-threshold mechanoreceptive neurons. The functional significance (sensory-discriminative, affective-motivational, cognitive-evaluative) of the closely spaced parasylvian cortical areas in acute and chronic pain is only poorly understood. It is likely that some of these areas are involved in sensory-limbic projection pathways that may subserve the recognition of potentially tissue damaging stimuli as well as pain memory.

Pain sensitivity alterations as a function of lesion location in the parasylvian cortex

Abstract: Six patients with lesions involving parasylvian cerebral cortex were evaluated for their pain thresholds using contact heat (all six) and sharp probes that evoke pin-prick pain (4/6). Without knowledge of the sensory status of the individuals, two of the authors evaluated the MRIs of these patients, and determined to what extent the following cerebral regions were involved in the lesion: anterior insula, posterior insula, retroinsula, and parietal operculum. Each patient's lesion encompassed at least two of these regions. Three individuals demonstrated significant laterality differences in pain sensitivity, with elevated thresholds on the hand contralateral to his/her lesion. The common feature in these cases was the inclusion of the parietal operculum and posterior insula. The three other cases showed no evidence of abnormal pain thresholds. The common feature of these cases was the apparent sparing of the parietal operculum. Thus, this series of cases points to the significance of the parietal operculum, either alone or with adjacent posterior insula, for normal pain thresholds. In comparison, extensive involvement of the anterior insula in two cases was not associated with abnormal pain thresholds. Four of the six patients were also evaluated with a cold pain tolerance test, which presumably involves more affective/motivational aspects of pain than threshold tests. Only two of these patients showed greater tolerance contralaterally versus ipsilaterally, and theirs were the two lesions of the four with involvement of a large part of the insula. This result supports the theory that the insula's involvement in nociceptive processing is related to the affective/motivational aspect of pain.

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

Abstract: 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.

Principles of Neural Science

Abstract: I have developed "tennis elbow" from lugging this book around the past four weeks, but it is worth the pain, the effort, and the aspirin. It is also worth the (relatively speaking) bargain price. Including appendixes, this book contains 894 pages of text. The entire panorama of the neural sciences is surveyed and examined, and it is comprehensive in its scope, from genomes to social behaviors. The editors explicitly state that the book is designed as "an introductory text for students of biology, behavior, and medicine," but it is hard to imagine any audience, interested in any fragment of neuroscience at any level of sophistication, that would not enjoy this book. The editors have done a masterful job of weaving together the biologic, the behavioral, and the clinical sciences into a single tapestry in which everyone from the molecular biologist to the practicing psychiatrist can find and appreciate his or

How do you feel? Interoception: the sense of the physiological condition of the body.

Abstract: As humans, we perceive feelings from our bodies that relate our state of well-being, our energy and stress levels, our mood and disposition. How do we have these feelings? What neural processes do they represent? Recent functional anatomical work has detailed an afferent neural system in primates and in humans that represents all aspects of the physiological condition of the physical body. This system constitutes a representation of 'the material me', and might provide a foundation for subjective feelings, emotion and self-awareness.

The Biopsychosocial Approach to Chronic Pain: Scientific Advances and Future Directions

Abstract: The prevalence and cost of chronic pain is a major physical and mental health care problem in the United States today. As a result, there has been a recent explosion of research on chronic pain, with significant advances in better understanding its etiology, assessment, and treatment. The purpose of the present article is to provide a review of the most noteworthy developments in the field. The biopsychosocial model is now widely accepted as the most heuristic approach to chronic pain. With this model in mind, a review of the basic neuroscience processes of pain (the bio part of biopsychosocial), as well as the psychosocial factors, is presented. This spans research on how psychological and social factors can interact with brain processes to influence health and illness as well as on the development of new technologies, such as brain imaging, that provide new insights into brain-pain mechanisms.