The Experts below are selected from a list of 27 Experts worldwide ranked by ideXlab platform
Shivanand P. Lad - One of the best experts on this subject based on the ideXlab platform.
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Structural mapping with fiber tractography of the human Cuneate Fasciculus at microscopic resolution in cervical region.
NeuroImage, 2019Co-Authors: Ahmet Fatih Atik, Evan Calabrese, Robert Gramer, Syed M. Adil, Shervin Rahimpour, Promila Pagadala, G. Allan Johnson, Shivanand P. LadAbstract:Abstract Human spinal white matter tract anatomy has been mapped using post mortem histological information with the help of molecular tracing studies in animal models. This study used 7 Tesla diffusion MR tractography on a human cadaver that was harvested 24 hours post mortem to evaluate Cuneate Fasciculus anatomy in cervical spinal cord. Based on this method, for the first time much more nuanced tractographic anatomy was used to investigate possible new routes for Cuneate Fasciculus in the posterior and lateral funiculus. Additionally, current molecular tracing studies were reviewed, and confirmatory data was presented along with our radiological results. Both studies confirm that upon entry to the spinal cord, upper cervical level tracts (C1-2-3) travel inside lateral funiculus and lower level tracts travel medially inside the posterior funiculus after entry at posterolateral sulcus which is different than traditional knowledge of having Cuneate Fasciculus tracts concentrated in the lateral part of posterior funiculus.
Ahmet Fatih Atik - One of the best experts on this subject based on the ideXlab platform.
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Structural mapping with fiber tractography of the human Cuneate Fasciculus at microscopic resolution in cervical region.
NeuroImage, 2019Co-Authors: Ahmet Fatih Atik, Evan Calabrese, Robert Gramer, Syed M. Adil, Shervin Rahimpour, Promila Pagadala, G. Allan Johnson, Shivanand P. LadAbstract:Abstract Human spinal white matter tract anatomy has been mapped using post mortem histological information with the help of molecular tracing studies in animal models. This study used 7 Tesla diffusion MR tractography on a human cadaver that was harvested 24 hours post mortem to evaluate Cuneate Fasciculus anatomy in cervical spinal cord. Based on this method, for the first time much more nuanced tractographic anatomy was used to investigate possible new routes for Cuneate Fasciculus in the posterior and lateral funiculus. Additionally, current molecular tracing studies were reviewed, and confirmatory data was presented along with our radiological results. Both studies confirm that upon entry to the spinal cord, upper cervical level tracts (C1-2-3) travel inside lateral funiculus and lower level tracts travel medially inside the posterior funiculus after entry at posterolateral sulcus which is different than traditional knowledge of having Cuneate Fasciculus tracts concentrated in the lateral part of posterior funiculus.
Amassian, Vahe E. - One of the best experts on this subject based on the ideXlab platform.
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Response of Forelimb Guard Hair Afferent Units to Air-Jet Stimulation of Entire Receptive Field
SelectedWorks, 2013Co-Authors: Goldfinger, Melvyn D., Amassian, Vahe E.Abstract:1. In anesthetized, immobilized cats, individual axonal responses to movement of forelimb G hairs were recorded in the ipsilateral Cuneate Fasciculus at C1-C2 with a glass-insulated tungsten microelectrode. Several test criteria were used to identify primary afferent axons among the recorded neurons. 2. The output discharge in the parent sensory axon during continuous air-jet stimulation of the entire receptive field was irregular and was usually maintained. Criteria for statistical stability were introduced, permitting an analysis of the response as a stable point process. 3. The main interspike interval during the response to maximal air-jet stimulation ranged in different units from 4 to 100 ms, with a transition zone near 20 ms (50/s) between short and long mean interval units. Long and short mean interval units tended to be related to G2- and G1-type hair receptors, respectively. 4. In both short and long mean interval units, the interspike-interval distribution (IID) had a dead time (usually 2-4 ms), a sigmoidal rising limb, a single mode, and a monotonic falling limb, a single mode, and a monotonic falling limb. In short mean interval units, the decrement of the falling limb was described by a single exponential. 5. The value of the standard deviation of the IID was a little less than that of the mean interval minus dead time, the inequality probably resulting from the finite duration of the rising limb and, in long mean interval units, the nonexponential falling limb. 6. Joint interval analysis revealed that successive intervals were independent except in short mean interval units, where the shortest intervals tended to be followed by intervals shorter than the mean. 7. The expectation density function did not reveal any periods in the output discharge. In short mean interval units, a constant mean (plateau) level was attained after a finite rise time and usually one or more overshooting-undershooting sequences. In long mean interval units, the expectation density function monotonically rose to the plateau level. 8. Reducing the air-jet intensity caused an increase in mean interval of discharge and in standard deviation of the IID and slowed the rise time of the expectation density function to the plateau level. 9. Similarities and differences between the whole-field response to air-jet stimulation and the Poisson process are discussed
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Contributions by Individual Guard Hairs and Their Interactions in Response of Forelimb Guard Hair Afferent Unit
SelectedWorks, 2013Co-Authors: Goldfinger, Melvyn D., Amassian, Vahe E.Abstract:1. In anesthetized, immobilized cats, single primary afferent axonal responses to movement of forelimb G hairs were recorded in the ipsilateral Cuneate Fasciculus with a glass-insulated tungsten microelectrode. 2. One or more innervated receptive-field G hairs were isolated with a thin shield, which prevented all other receptive-field hairs from being driven by the test mechanical stimulus. 3. Spike trains were elicited by mechanical stimulation of one or more innervated hairs either by continuous air jet or by trains of fixed displacement transients and were recorded either in the steady state or over an isochronal period beginning with the onset of the maintained mechanical stimulation. 4. Maximal intensity air-jet stimulation of one hair evoked a mean discharge frequency that was significantly lower than that evoked by applying the same stimulus to the entire receptive field. 5. Steady-state discharge evoked by air- jet stimulation of a single hair had a) an inter- spike interval distribution with a dead time, a monotonic rising limb to a single mode, and a monotonic falling limb; and b) serial interspike-interval independence except for the shortest intervals. 6. The isochronal mean frequency elicited by maximal intensity air-jet stimulation of pairs of innervated hairs was less than that elicited by whole-field stimulation. While the dual-hair response frequency was greater than that elicited by either hair alone, it was either less than, greater than, or close to the sum of the individually elicited frequencies. 7. Comparison of the dual-hair-evoked spike train with that which resulted from the superposition of the two individually evoked spike trains revealed that during dual-hair stimulation, there is: a) a deficit of the shortest predicted intervals; and b) either less than, greater than, or approximately the same distribution of other classes of predicted intervals. The relative amounts of a and b determine the degree of non-arithmetic summation of constituent frequencies (item 6, above). 8. Electrical stimulation of the parent afferent axon elicited a long-duration cycle of elevated mechanical threshold as tested from a single innervated hair. However, electrical stimulation of the parent axon during continuous air-jet stimulation did not significantly change the pattern of air-jet-evoked spike generation in the poststimulus histogram except for the absence of an early greater-than-steady-state elevation of conditional firing probability for short mean interval units. 9. Using brief triangular displacement of innervated hairs at sufficiently high periodic repetition rates, the output spike frequency evoked by driving N hairs was found to be less than that evoked by driving N + 1 hairs. The interspike-interval distribution (IID) of the spike train evoked by such stimulation has a mode at the interstimulus interval or multiples thereof. 10. The marked difference between IIDs of responses to air-jet and periodic repetitive stimuli most likely reflects aperiodic components of hair movement under the air jet. 11. Processing of information by hair follicle and touch afferent units is contrasted. 12. Summation of generator potentials or of blocked impulses at sites of probabilistic transmission is proposed as the explanation of the observed facilitation; the branch points in the arborization of the parent axon are proposed as critical sites of probabilistic transmission. 13. The output discharge frequency in the parent axon is modeled by a set of equations that separately describe the effects of facilitation and refractoriness
Goldfinger, Melvyn D. - One of the best experts on this subject based on the ideXlab platform.
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Contributions by Individual Guard Hairs and Their Interactions in Response of Forelimb Guard Hair Afferent Unit
SelectedWorks, 2013Co-Authors: Goldfinger, Melvyn D., Amassian, Vahe E.Abstract:1. In anesthetized, immobilized cats, single primary afferent axonal responses to movement of forelimb G hairs were recorded in the ipsilateral Cuneate Fasciculus with a glass-insulated tungsten microelectrode. 2. One or more innervated receptive-field G hairs were isolated with a thin shield, which prevented all other receptive-field hairs from being driven by the test mechanical stimulus. 3. Spike trains were elicited by mechanical stimulation of one or more innervated hairs either by continuous air jet or by trains of fixed displacement transients and were recorded either in the steady state or over an isochronal period beginning with the onset of the maintained mechanical stimulation. 4. Maximal intensity air-jet stimulation of one hair evoked a mean discharge frequency that was significantly lower than that evoked by applying the same stimulus to the entire receptive field. 5. Steady-state discharge evoked by air- jet stimulation of a single hair had a) an inter- spike interval distribution with a dead time, a monotonic rising limb to a single mode, and a monotonic falling limb; and b) serial interspike-interval independence except for the shortest intervals. 6. The isochronal mean frequency elicited by maximal intensity air-jet stimulation of pairs of innervated hairs was less than that elicited by whole-field stimulation. While the dual-hair response frequency was greater than that elicited by either hair alone, it was either less than, greater than, or close to the sum of the individually elicited frequencies. 7. Comparison of the dual-hair-evoked spike train with that which resulted from the superposition of the two individually evoked spike trains revealed that during dual-hair stimulation, there is: a) a deficit of the shortest predicted intervals; and b) either less than, greater than, or approximately the same distribution of other classes of predicted intervals. The relative amounts of a and b determine the degree of non-arithmetic summation of constituent frequencies (item 6, above). 8. Electrical stimulation of the parent afferent axon elicited a long-duration cycle of elevated mechanical threshold as tested from a single innervated hair. However, electrical stimulation of the parent axon during continuous air-jet stimulation did not significantly change the pattern of air-jet-evoked spike generation in the poststimulus histogram except for the absence of an early greater-than-steady-state elevation of conditional firing probability for short mean interval units. 9. Using brief triangular displacement of innervated hairs at sufficiently high periodic repetition rates, the output spike frequency evoked by driving N hairs was found to be less than that evoked by driving N + 1 hairs. The interspike-interval distribution (IID) of the spike train evoked by such stimulation has a mode at the interstimulus interval or multiples thereof. 10. The marked difference between IIDs of responses to air-jet and periodic repetitive stimuli most likely reflects aperiodic components of hair movement under the air jet. 11. Processing of information by hair follicle and touch afferent units is contrasted. 12. Summation of generator potentials or of blocked impulses at sites of probabilistic transmission is proposed as the explanation of the observed facilitation; the branch points in the arborization of the parent axon are proposed as critical sites of probabilistic transmission. 13. The output discharge frequency in the parent axon is modeled by a set of equations that separately describe the effects of facilitation and refractoriness
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Response of Forelimb Guard Hair Afferent Units to Air-Jet Stimulation of Entire Receptive Field
SelectedWorks, 2013Co-Authors: Goldfinger, Melvyn D., Amassian, Vahe E.Abstract:1. In anesthetized, immobilized cats, individual axonal responses to movement of forelimb G hairs were recorded in the ipsilateral Cuneate Fasciculus at C1-C2 with a glass-insulated tungsten microelectrode. Several test criteria were used to identify primary afferent axons among the recorded neurons. 2. The output discharge in the parent sensory axon during continuous air-jet stimulation of the entire receptive field was irregular and was usually maintained. Criteria for statistical stability were introduced, permitting an analysis of the response as a stable point process. 3. The main interspike interval during the response to maximal air-jet stimulation ranged in different units from 4 to 100 ms, with a transition zone near 20 ms (50/s) between short and long mean interval units. Long and short mean interval units tended to be related to G2- and G1-type hair receptors, respectively. 4. In both short and long mean interval units, the interspike-interval distribution (IID) had a dead time (usually 2-4 ms), a sigmoidal rising limb, a single mode, and a monotonic falling limb, a single mode, and a monotonic falling limb. In short mean interval units, the decrement of the falling limb was described by a single exponential. 5. The value of the standard deviation of the IID was a little less than that of the mean interval minus dead time, the inequality probably resulting from the finite duration of the rising limb and, in long mean interval units, the nonexponential falling limb. 6. Joint interval analysis revealed that successive intervals were independent except in short mean interval units, where the shortest intervals tended to be followed by intervals shorter than the mean. 7. The expectation density function did not reveal any periods in the output discharge. In short mean interval units, a constant mean (plateau) level was attained after a finite rise time and usually one or more overshooting-undershooting sequences. In long mean interval units, the expectation density function monotonically rose to the plateau level. 8. Reducing the air-jet intensity caused an increase in mean interval of discharge and in standard deviation of the IID and slowed the rise time of the expectation density function to the plateau level. 9. Similarities and differences between the whole-field response to air-jet stimulation and the Poisson process are discussed
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Poisson-Process Electrical Stimulation: Circuit and Axonal Responses
SelectedWorks, 2012Co-Authors: Moradmand K., Goldfinger, Melvyn D.Abstract:This work describes a simple circuit which generated a highly Poisson-like sequence of pulses. Resistor noise was amplified in three series stages followed by rectification through a relatively large shunt resistance. This yielded a sequence of variable-amplitude transients, which were inverted, amplified with DC adjustment, and fed into a Schmitt trigger/multivibrator chip for pulse generation. The pulse generation frequency was modulated by the amplification of the rectified transients. The stochastic characteristics of the output pulse train were Poisson-like over a wide frequency range, as assessed using the interevent interval distribution and expectation density as steady-state and real-time estimators, respectively. In separate tests, the output pulse train was applied to forelimb cutaneous axons of the anesthetized cat; trains of elicited propagating action potentials were recorded extracellularly from individual G1 axons in the Cuneate Fasciculus. The stochastic properties of the action potential train differed from those of the stimulus, with longer deadtime, lower mean rate, and an early expectation density peak. These physiological responses to circuit output were similar to those elicited by other generators of Poisson-like stimulation
Evan Calabrese - One of the best experts on this subject based on the ideXlab platform.
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Structural mapping with fiber tractography of the human Cuneate Fasciculus at microscopic resolution in cervical region.
NeuroImage, 2019Co-Authors: Ahmet Fatih Atik, Evan Calabrese, Robert Gramer, Syed M. Adil, Shervin Rahimpour, Promila Pagadala, G. Allan Johnson, Shivanand P. LadAbstract:Abstract Human spinal white matter tract anatomy has been mapped using post mortem histological information with the help of molecular tracing studies in animal models. This study used 7 Tesla diffusion MR tractography on a human cadaver that was harvested 24 hours post mortem to evaluate Cuneate Fasciculus anatomy in cervical spinal cord. Based on this method, for the first time much more nuanced tractographic anatomy was used to investigate possible new routes for Cuneate Fasciculus in the posterior and lateral funiculus. Additionally, current molecular tracing studies were reviewed, and confirmatory data was presented along with our radiological results. Both studies confirm that upon entry to the spinal cord, upper cervical level tracts (C1-2-3) travel inside lateral funiculus and lower level tracts travel medially inside the posterior funiculus after entry at posterolateral sulcus which is different than traditional knowledge of having Cuneate Fasciculus tracts concentrated in the lateral part of posterior funiculus.
