Harvey Swadlow - Academia.edu (original) (raw)

Papers by Harvey Swadlow

Taylor & Francis eBooks, Feb 16, 2010

The Journal of Neuroscience, Apr 17, 2020

Science, Nov 26, 1982

Microelectrode recordings were used in conjunction with antidromic activation to monitor impulse ... more Microelectrode recordings were used in conjunction with antidromic activation to monitor impulse conduction along individual mammalian cerebral axons for periods of up to 165 days. Approximately half of the axons studied showed a stable conduction velocity and stable aftereffects of impulse activity. The remaining axons showed slow and progressive increases or decreases in conduction velocity overtime. In these latter axons, changes in the magnitude of the aftereffects of impulse conduction were far less pronounced than were changes in axonal conduction velocity.

Experimental Neurology, Feb 1, 1981

ABSTRACT

Brain Behavior and Evolution, 1980

Previous studies have shown interhemispheric visual connections in primates to be limited to extr... more Previous studies have shown interhemispheric visual connections in primates to be limited to extrastriate cortex. Using the retrograde transport technique of horseradish peroxidase, we show that in the prosimian primate Galago senegalensis both striate and extrastriate cortex contribute a substantial projection to the contralateral hemisphere. Thus, the lack of an interhemispheric projection from area 17 is not a characteristic of primates and may be peculiar to only a few primate species.

Elsevier eBooks, 2005

Thalamocortical (TC) neurons form only a small percentage of the synapses onto neurons of cortica... more Thalamocortical (TC) neurons form only a small percentage of the synapses onto neurons of cortical layer 4, but the response properties of these cortical neurons are arguably dominated by thalamic input. This discrepancy is explained, in part, by studies showing that TC synapses are of high efficacy. However, TC synapses display activity-dependent depression. Because of this, in vitro measures of synaptic efficacy will not reflect the situation in vivo, where different neuronal populations have widely varying levels of "spontaneous" activity. Indeed, TC neurons of awake subjects generate high rates of spontaneous activity that would be expected, in a depressing synapse, to result in a chronic state of synaptic depression. Here, we review recent work in the somatosensory thalamocortical system of awake rabbits in which the relationship between TC spike timing and TC synaptic efficacy was examined during both thalamic "relay mode" (alert state) and "burst mode" (drowsy state). Two largely independent methodological approaches were used. First, we employed cross-correlation methods to examine the synaptic impact of single TC "barreloid" neurons on a single neuronal subtype in the topographically aligned layer 4 "barrel" - putative fast-spike inhibitory interneurons. We found that the initial spike of a TC burst, as well as isolated TC spikes with long preceding interspike intervals (ISIs) elicited postsynaptic action potentials far more effectively than did TC impulses with short ISIs. Our second approach took a broader view of the postsynaptic impact of TC impulses. In these experiments we examined spike-triggered extracellular field potentials and synaptic currents (using current source-density analysis) generated through the depths of a cortical barrel column by the impulses of single topographically aligned TC neurons. We found that (a) closely neighboring TC neurons may elicit very different patterns of monosynaptic activation within layers 4 and 6 of the aligned column, (b) synaptic currents elicited by TC impulses with long preceding ISIs were greatly enhanced in both of these layers, and (c) the degree of this enhancement differed reliably among neighboring TC neurons but, for a given neuron, was very similar in layers 4 and 6. Thus, results generated by both methodological approaches are consistent with the presence of a chronic depression at the awake TC synapse that is relieved by long ISIs. Since long ISIs necessarily precede TC "bursts", our results are consistent with the notion that these events powerfully activate cortical circuits.

Proceedings of the National Academy of Sciences of the United States of America, Dec 1, 1975

Brain Research Reviews, Aug 1, 1983

The Journal of Neuroscience, Feb 1, 2003

Experimental Brain Research, Jan 10, 2000

Journal of Neurophysiology, Jul 1, 1985

The intrinsic stability of the rabbit eye was exploited to enable receptive-field analysis of LGN... more The intrinsic stability of the rabbit eye was exploited to enable receptive-field analysis of LGNd neurons and optic tract axons in the awake, unparalyzed state. We found eye position to remain within a range of less than 1.0 degrees for periods of 4-5 min, and in some cases for periods in excess of 10 min. Such stability is comparable to that seen in awake monkeys that have been trained to fixate. Receptive fields of dorsal lateral geniculate nucleus (LGNd) neurons were analyzed, and approximately 84% were concentrically organized. This is a higher value than previously reported in this species. In addition, the receptive-field centers of concentric cells were much smaller than those previously reported (mean diameter = 2.5 degrees). Most remaining neurons in the LGNd were either directionally selective (6.5%) or motion/uniform (6.5%). Concentric cells were classified as sustained or transient based on response duration to standing contrast. In the LGNd the receptive fields of sustained concentric cells were predominantly near the horizontal meridian, within the representation of the visual streak, while the receptive-field positions of transient concentric cells were more prevalent in the upper visual field. In the optic tract the receptive-field positions of both sustained and transient cells were more evenly distributed than was seen in the LGNd. Sustained and transient concentric cells in LGNd showed primarily nonlinear spatial summation. The receptive-field properties of LGNd neurons were related to geniculocortical antidromic latency. Most LGNd neurons of all receptive-field classes projected axons to the visual cortex. Thus, any intrinsic interneurons in the rabbit LGNd may have receptive-field properties similar to those of some principal neurons. There was significant overlap in the distribution of antidromic latencies in neurons of different receptive-field classes. Concentric sustained neurons, however, did conduct somewhat more slowly than did concentric transient neurons. Nonvisual sensory stimuli that resulted in EEG arousal (hippocampal theta activity) had a profound effect on the response duration of most (28/32) sustained concentric neurons. For these cells, the sustained response to standing contrast began to diminish and sometimes disappeared after 2-15 s. However, arousing stimuli that resulted in hippocampal theta activity reestablished the sustained response. Such arousing stimuli usually had little or no effect on the discharge of the cell in the absence of visual stimuli. Arousing stimuli had no effect on optic tract axons with sustained concentric receptive-field properties.(ABSTRACT TRUNCATED AT 400 WORDS)

Physiology & Behavior, 1969

... Printed in Great Britain BRIEF COMMUNICATION SplitBrain: Stereotaxic Section of Telencephalic... more ... Printed in Great Britain BRIEF COMMUNICATION SplitBrain: Stereotaxic Section of Telencephalic and Brain Stem Structures in RabbitsI HARVEY SWADLOWs AND ... frozen, and sectioned in coronal sections at 50 t using a modification of the procedure of Guzman, Alcarez and ...

Journal of Neurophysiology, Apr 1, 1996

1. Latencies to peripheral sensory stimulation were examined in four classes of antidromically id... more 1. Latencies to peripheral sensory stimulation were examined in four classes of antidromically identified efferent neurons in the primary somatosensory cortex (S1) of awake rabbits. Both suprathreshold responses (action potentials) and subthreshold responses were examined. Subthreshold responses were examined by monitoring the thresholds of efferent neurons to juxtasomal current pulses (JSCPs) delivered through the recording microelectrode (usually 1-3 microA). Through the use of this method, excitatory postsynaptic potentials (EPSPs) and inhibitory postsynaptic potentials (IPSPs) were manifested as decreases and increases in threshold, respectively. Efferent populations examined included callosal (CC) neurons, ipsilateral corticocortical (C-IC) neurons, and descending corticofugal neurons of layer 5 (CF-5) and layer 6 (CF-6). Very brief air puffs (rise and fall times 0.6 ms) were delivered to the receptor periphery via a high-speed solenoid valve. 2. Whereas all CF-5 neurons had demonstrable suprathreshold excitatory and/or inhibitory responses to peripheral stimulation, most CC, C-IC, and CF-6 neurons did not. CC and CF-6 neurons that yielded no suprathreshold response to the stimulus had lower axonal conduction velocities than those that did respond (P < 0.0001 in both cases). However, subthreshold receptive fields could be demonstrated in many of the otherwise unresponsive CC (81%), C-IC (88%), and CF-6 (43%) neurons. The subthreshold responses usually consisted of an initial excitatory component (a decrease in the threshold to the JSCP) and a subsequent long-duration (> 80 ms) inhibitory component. A few neurons (1 CC, 1 C-IC, and 5 CF-6) showed an initial short latency inhibitory response in the absence of any excitatory component. 3. Some CC and C-IC neurons yielded supra- and/or subthreshold responses to peripheral stimulation at latencies of 6.1-7 ms. All such neurons were found at intermediate cortical depths (thought to correspond to deep layer 2-3 through layer 5). It is argued that such latencies are indicative of monosynaptic activation via thalamic afferents. Very superficial CC and C-IC neurons, and all CF-6 neurons responded to latencies of > 7 ms. All CF-5 neurons responded to latencies of > 8 ms, although many were found at the same depth as the deeper CC and C-IC neurons that responded at monosynaptic latencies. These results indicate that cortical cell type as well as laminar position are important factors that determine the sequence of intracortical neuronal activation after peripheral sensory stimulation.

Archives of neurology, Feb 1, 1980

The splenium of the corpus callosum of a primate (Macaca mulatta), examined with the electron mic... more The splenium of the corpus callosum of a primate (Macaca mulatta), examined with the electron microscope, was found to contain both myelinated and nonmyelinated axons. The majority of nonmyelinated axons had diameters of less tha 0.25 micron. On the basis of this diameter distribution, it is expected that many callosal axons conduct impulses at velocities of less than 1 m/s and that interhemispheric conduction times for some callosal axons are at least 30 ms and possibly much longer.

Journal of Neuroscience Methods, Feb 1, 1998

Although simple in concept, reliable antidromic identification of efferent populations poses nume... more Although simple in concept, reliable antidromic identification of efferent populations poses numerous technical challenges and is subject to a host of sampling biases, most of which select against the detection of the neurons with slowly conducting axons. This problem is particularly acute in studies of the neocortex. Many neocortical efferent systems have large sub-populations with very slowly conducting, nonmyelinated axons and these elements have been relatively neglected in antidromic studies of neocortical neurons. The present review attempts to redress this problem by analyzing the steps that must necessarily precede antidromic identification and the sampling biases associated with each of these steps. These steps include (1) initial recognition that the microelectrode is near a neuron; (2) activation of the efferent axon via the stimulating electrode; (3) conduction of the antidromic impulse from stimulation site to soma; (4) detection of the antidromic spike in the extracellular record and (5) discriminating antidromic from synaptic activation. Experimental strategies are suggested for minimizing the sampling biases associated with each of these steps; most of which can be reduced or eliminated by appropriate experimental procedures. Careful attention to such procedures will make it possible to better understand the nature and function of the information flow along the very slowly conducting axonal systems of the neocortex.

Journal of comparative neurology, Dec 20, 1981

Several efferent systems of visual area I in Dutch rabbits were studied with anatomical (horserad... more Several efferent systems of visual area I in Dutch rabbits were studied with anatomical (horseradish peroxidase) and physiological (antidromic) methods. Anatomical studies provided information regarding the laminar origin of the projections to the contralateral hemisphere, visual area II, the dorsal lateral geniculate nucleus, and the superior colliculus. Physiological studies provided information regarding conduction velocities and multiple destinations of efferent axons. Both the callosal projection and the projection to V-II were shown to originate primarily in layer II-III. However, approximately 10-20% of the callosal projection and 20-40% of the projection to V-II originated in layers IV and V. In contrast, the projection to the dorsal lateral geniculate nucleus originated nearly exclusively in layer VI, while corticotectal neurons occurred primarily in layer V. A significant number of corticotectal neurons were, however, found in layer IV. Thus, the above efferent systems were found to differ in their principal laminar origin and in the diffuseness of that origin. The origins of corticocortical projections were considerably more diffuse than those of corticofugal projections. In addition to differences in laminar origin, efferent systems also differed significantly in the conduction velocities of their axons. The projection to visual area II and to the lateral geniculate nucleus consisted primarily of very slowly conducting axons, while the projection to the superior colliculus was fast conduction. The callosal projection consisted of both slow and fact conduction axons. Finally, the question of branching of V-I efferent axons was addressed. Although the laminar origin of the projections to the contralateral hemisphere and to visual area II overlapped considerably, none of these corticocortical axons could be shown to project to both locations or to a subcortical destination. In contrast, approximately one-third of corticotectal axons were shown to project a collateral into the thalamus. Although the destination of this collateral is unclear, it is medial to the lateral geniculate nucleus and may be the pulvinar.

Annual review of biophysics and bioengineering, Jun 1, 1980

Nature Neuroscience, Jul 1, 2002

The corpus callosum of most mammals is comprised of both myelinated and nonmyelinated axons, most... more The corpus callosum of most mammals is comprised of both myelinated and nonmyelinated axons, most of which are less then 1 μm in diameter (Fleischhauer and Wartenberg, 1967; Seggie and Berry, 1972; Tomasch, 1954; Tomasch and MacMillan, 1957; Waxman and Swadlow, 1976a). Characteristics of impulse conduction along such axons in the central nervous system are relatively unstudied. In the present chapter we review our work on the ultrastructure and conduction properties of visual callosal axons of the rabbit and also present preliminary data on the conduction properties of callosal axons of the macaque monkey.

Taylor & Francis eBooks, Feb 16, 2010

The Journal of Neuroscience, Apr 17, 2020

Science, Nov 26, 1982

Microelectrode recordings were used in conjunction with antidromic activation to monitor impulse ... more Microelectrode recordings were used in conjunction with antidromic activation to monitor impulse conduction along individual mammalian cerebral axons for periods of up to 165 days. Approximately half of the axons studied showed a stable conduction velocity and stable aftereffects of impulse activity. The remaining axons showed slow and progressive increases or decreases in conduction velocity overtime. In these latter axons, changes in the magnitude of the aftereffects of impulse conduction were far less pronounced than were changes in axonal conduction velocity.

Experimental Neurology, Feb 1, 1981

ABSTRACT

Brain Behavior and Evolution, 1980

Previous studies have shown interhemispheric visual connections in primates to be limited to extr... more Previous studies have shown interhemispheric visual connections in primates to be limited to extrastriate cortex. Using the retrograde transport technique of horseradish peroxidase, we show that in the prosimian primate Galago senegalensis both striate and extrastriate cortex contribute a substantial projection to the contralateral hemisphere. Thus, the lack of an interhemispheric projection from area 17 is not a characteristic of primates and may be peculiar to only a few primate species.

Elsevier eBooks, 2005

Thalamocortical (TC) neurons form only a small percentage of the synapses onto neurons of cortica... more Thalamocortical (TC) neurons form only a small percentage of the synapses onto neurons of cortical layer 4, but the response properties of these cortical neurons are arguably dominated by thalamic input. This discrepancy is explained, in part, by studies showing that TC synapses are of high efficacy. However, TC synapses display activity-dependent depression. Because of this, in vitro measures of synaptic efficacy will not reflect the situation in vivo, where different neuronal populations have widely varying levels of "spontaneous" activity. Indeed, TC neurons of awake subjects generate high rates of spontaneous activity that would be expected, in a depressing synapse, to result in a chronic state of synaptic depression. Here, we review recent work in the somatosensory thalamocortical system of awake rabbits in which the relationship between TC spike timing and TC synaptic efficacy was examined during both thalamic "relay mode" (alert state) and "burst mode" (drowsy state). Two largely independent methodological approaches were used. First, we employed cross-correlation methods to examine the synaptic impact of single TC "barreloid" neurons on a single neuronal subtype in the topographically aligned layer 4 "barrel" - putative fast-spike inhibitory interneurons. We found that the initial spike of a TC burst, as well as isolated TC spikes with long preceding interspike intervals (ISIs) elicited postsynaptic action potentials far more effectively than did TC impulses with short ISIs. Our second approach took a broader view of the postsynaptic impact of TC impulses. In these experiments we examined spike-triggered extracellular field potentials and synaptic currents (using current source-density analysis) generated through the depths of a cortical barrel column by the impulses of single topographically aligned TC neurons. We found that (a) closely neighboring TC neurons may elicit very different patterns of monosynaptic activation within layers 4 and 6 of the aligned column, (b) synaptic currents elicited by TC impulses with long preceding ISIs were greatly enhanced in both of these layers, and (c) the degree of this enhancement differed reliably among neighboring TC neurons but, for a given neuron, was very similar in layers 4 and 6. Thus, results generated by both methodological approaches are consistent with the presence of a chronic depression at the awake TC synapse that is relieved by long ISIs. Since long ISIs necessarily precede TC "bursts", our results are consistent with the notion that these events powerfully activate cortical circuits.

Proceedings of the National Academy of Sciences of the United States of America, Dec 1, 1975

Brain Research Reviews, Aug 1, 1983

The Journal of Neuroscience, Feb 1, 2003

Experimental Brain Research, Jan 10, 2000

Journal of Neurophysiology, Jul 1, 1985

The intrinsic stability of the rabbit eye was exploited to enable receptive-field analysis of LGN... more The intrinsic stability of the rabbit eye was exploited to enable receptive-field analysis of LGNd neurons and optic tract axons in the awake, unparalyzed state. We found eye position to remain within a range of less than 1.0 degrees for periods of 4-5 min, and in some cases for periods in excess of 10 min. Such stability is comparable to that seen in awake monkeys that have been trained to fixate. Receptive fields of dorsal lateral geniculate nucleus (LGNd) neurons were analyzed, and approximately 84% were concentrically organized. This is a higher value than previously reported in this species. In addition, the receptive-field centers of concentric cells were much smaller than those previously reported (mean diameter = 2.5 degrees). Most remaining neurons in the LGNd were either directionally selective (6.5%) or motion/uniform (6.5%). Concentric cells were classified as sustained or transient based on response duration to standing contrast. In the LGNd the receptive fields of sustained concentric cells were predominantly near the horizontal meridian, within the representation of the visual streak, while the receptive-field positions of transient concentric cells were more prevalent in the upper visual field. In the optic tract the receptive-field positions of both sustained and transient cells were more evenly distributed than was seen in the LGNd. Sustained and transient concentric cells in LGNd showed primarily nonlinear spatial summation. The receptive-field properties of LGNd neurons were related to geniculocortical antidromic latency. Most LGNd neurons of all receptive-field classes projected axons to the visual cortex. Thus, any intrinsic interneurons in the rabbit LGNd may have receptive-field properties similar to those of some principal neurons. There was significant overlap in the distribution of antidromic latencies in neurons of different receptive-field classes. Concentric sustained neurons, however, did conduct somewhat more slowly than did concentric transient neurons. Nonvisual sensory stimuli that resulted in EEG arousal (hippocampal theta activity) had a profound effect on the response duration of most (28/32) sustained concentric neurons. For these cells, the sustained response to standing contrast began to diminish and sometimes disappeared after 2-15 s. However, arousing stimuli that resulted in hippocampal theta activity reestablished the sustained response. Such arousing stimuli usually had little or no effect on the discharge of the cell in the absence of visual stimuli. Arousing stimuli had no effect on optic tract axons with sustained concentric receptive-field properties.(ABSTRACT TRUNCATED AT 400 WORDS)

Physiology & Behavior, 1969

... Printed in Great Britain BRIEF COMMUNICATION SplitBrain: Stereotaxic Section of Telencephalic... more ... Printed in Great Britain BRIEF COMMUNICATION SplitBrain: Stereotaxic Section of Telencephalic and Brain Stem Structures in RabbitsI HARVEY SWADLOWs AND ... frozen, and sectioned in coronal sections at 50 t using a modification of the procedure of Guzman, Alcarez and ...

Journal of Neurophysiology, Apr 1, 1996

1. Latencies to peripheral sensory stimulation were examined in four classes of antidromically id... more 1. Latencies to peripheral sensory stimulation were examined in four classes of antidromically identified efferent neurons in the primary somatosensory cortex (S1) of awake rabbits. Both suprathreshold responses (action potentials) and subthreshold responses were examined. Subthreshold responses were examined by monitoring the thresholds of efferent neurons to juxtasomal current pulses (JSCPs) delivered through the recording microelectrode (usually 1-3 microA). Through the use of this method, excitatory postsynaptic potentials (EPSPs) and inhibitory postsynaptic potentials (IPSPs) were manifested as decreases and increases in threshold, respectively. Efferent populations examined included callosal (CC) neurons, ipsilateral corticocortical (C-IC) neurons, and descending corticofugal neurons of layer 5 (CF-5) and layer 6 (CF-6). Very brief air puffs (rise and fall times 0.6 ms) were delivered to the receptor periphery via a high-speed solenoid valve. 2. Whereas all CF-5 neurons had demonstrable suprathreshold excitatory and/or inhibitory responses to peripheral stimulation, most CC, C-IC, and CF-6 neurons did not. CC and CF-6 neurons that yielded no suprathreshold response to the stimulus had lower axonal conduction velocities than those that did respond (P < 0.0001 in both cases). However, subthreshold receptive fields could be demonstrated in many of the otherwise unresponsive CC (81%), C-IC (88%), and CF-6 (43%) neurons. The subthreshold responses usually consisted of an initial excitatory component (a decrease in the threshold to the JSCP) and a subsequent long-duration (> 80 ms) inhibitory component. A few neurons (1 CC, 1 C-IC, and 5 CF-6) showed an initial short latency inhibitory response in the absence of any excitatory component. 3. Some CC and C-IC neurons yielded supra- and/or subthreshold responses to peripheral stimulation at latencies of 6.1-7 ms. All such neurons were found at intermediate cortical depths (thought to correspond to deep layer 2-3 through layer 5). It is argued that such latencies are indicative of monosynaptic activation via thalamic afferents. Very superficial CC and C-IC neurons, and all CF-6 neurons responded to latencies of > 7 ms. All CF-5 neurons responded to latencies of > 8 ms, although many were found at the same depth as the deeper CC and C-IC neurons that responded at monosynaptic latencies. These results indicate that cortical cell type as well as laminar position are important factors that determine the sequence of intracortical neuronal activation after peripheral sensory stimulation.

Archives of neurology, Feb 1, 1980

The splenium of the corpus callosum of a primate (Macaca mulatta), examined with the electron mic... more The splenium of the corpus callosum of a primate (Macaca mulatta), examined with the electron microscope, was found to contain both myelinated and nonmyelinated axons. The majority of nonmyelinated axons had diameters of less tha 0.25 micron. On the basis of this diameter distribution, it is expected that many callosal axons conduct impulses at velocities of less than 1 m/s and that interhemispheric conduction times for some callosal axons are at least 30 ms and possibly much longer.

Journal of Neuroscience Methods, Feb 1, 1998

Although simple in concept, reliable antidromic identification of efferent populations poses nume... more Although simple in concept, reliable antidromic identification of efferent populations poses numerous technical challenges and is subject to a host of sampling biases, most of which select against the detection of the neurons with slowly conducting axons. This problem is particularly acute in studies of the neocortex. Many neocortical efferent systems have large sub-populations with very slowly conducting, nonmyelinated axons and these elements have been relatively neglected in antidromic studies of neocortical neurons. The present review attempts to redress this problem by analyzing the steps that must necessarily precede antidromic identification and the sampling biases associated with each of these steps. These steps include (1) initial recognition that the microelectrode is near a neuron; (2) activation of the efferent axon via the stimulating electrode; (3) conduction of the antidromic impulse from stimulation site to soma; (4) detection of the antidromic spike in the extracellular record and (5) discriminating antidromic from synaptic activation. Experimental strategies are suggested for minimizing the sampling biases associated with each of these steps; most of which can be reduced or eliminated by appropriate experimental procedures. Careful attention to such procedures will make it possible to better understand the nature and function of the information flow along the very slowly conducting axonal systems of the neocortex.

Journal of comparative neurology, Dec 20, 1981

Several efferent systems of visual area I in Dutch rabbits were studied with anatomical (horserad... more Several efferent systems of visual area I in Dutch rabbits were studied with anatomical (horseradish peroxidase) and physiological (antidromic) methods. Anatomical studies provided information regarding the laminar origin of the projections to the contralateral hemisphere, visual area II, the dorsal lateral geniculate nucleus, and the superior colliculus. Physiological studies provided information regarding conduction velocities and multiple destinations of efferent axons. Both the callosal projection and the projection to V-II were shown to originate primarily in layer II-III. However, approximately 10-20% of the callosal projection and 20-40% of the projection to V-II originated in layers IV and V. In contrast, the projection to the dorsal lateral geniculate nucleus originated nearly exclusively in layer VI, while corticotectal neurons occurred primarily in layer V. A significant number of corticotectal neurons were, however, found in layer IV. Thus, the above efferent systems were found to differ in their principal laminar origin and in the diffuseness of that origin. The origins of corticocortical projections were considerably more diffuse than those of corticofugal projections. In addition to differences in laminar origin, efferent systems also differed significantly in the conduction velocities of their axons. The projection to visual area II and to the lateral geniculate nucleus consisted primarily of very slowly conducting axons, while the projection to the superior colliculus was fast conduction. The callosal projection consisted of both slow and fact conduction axons. Finally, the question of branching of V-I efferent axons was addressed. Although the laminar origin of the projections to the contralateral hemisphere and to visual area II overlapped considerably, none of these corticocortical axons could be shown to project to both locations or to a subcortical destination. In contrast, approximately one-third of corticotectal axons were shown to project a collateral into the thalamus. Although the destination of this collateral is unclear, it is medial to the lateral geniculate nucleus and may be the pulvinar.

Annual review of biophysics and bioengineering, Jun 1, 1980

Nature Neuroscience, Jul 1, 2002

The corpus callosum of most mammals is comprised of both myelinated and nonmyelinated axons, most... more The corpus callosum of most mammals is comprised of both myelinated and nonmyelinated axons, most of which are less then 1 μm in diameter (Fleischhauer and Wartenberg, 1967; Seggie and Berry, 1972; Tomasch, 1954; Tomasch and MacMillan, 1957; Waxman and Swadlow, 1976a). Characteristics of impulse conduction along such axons in the central nervous system are relatively unstudied. In the present chapter we review our work on the ultrastructure and conduction properties of visual callosal axons of the rabbit and also present preliminary data on the conduction properties of callosal axons of the macaque monkey.