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H A Swadlow

Publications and source records attributed to H A Swadlow.

At least 19 recordsLinked to original sources
PubMed1992

Monitoring the excitability of neocortical efferent neurons to direct activation by extracellular current pulses.

1. Extracellular action potentials were recorded from antidromically activated efferent neurons in visual, somatosensory, and motor cortex of the awake rabbit using low-impedance metal microelectrodes. Efferent neurons were also activated by current pulses delivered near the soma [juxtasomal current pulses (JSCPs)] through the recording microelectrode. Action potentials generated by JSCPs were not directly observed (because of the stimulus artifact), but were inferred with the use of a collision paradigm. Efferent populations studied include callosal neurons [CC (n = 80)], ipsilateral corticocortical neurons [C-IC (n = 21)], corticothalamic neurons of layer 6 [CF-6 (n = 57)], and descending corticofugal neurons of layer 5 [CF-5, corticotectal neurons of the visual cortex (n = 48)]. 2. Most CC neurons (45/46) and all C-IC (8/8) and CF-6 neurons (39/39) were directly activated by JSCPs at near-threshold intensities. Some CF-5 neurons (9/38), however, showed evidence of indirect activation. All efferent classes had similar current thresholds (means 1.85-2.10 microA) to direct activation by JSCPs, and thresholds were inversely related to extracellular spike amplitude. For each neuron, the range of JSCP intensities that generated response probabilities of between 0.2 and 0.8 was measured, and this "range of uncertainty" was significantly greater in CF-5 neurons (mean 32.7% of threshold) than in CC (mean 19.0%) or CF-6 (mean 20.4%) neurons. 3. Several factors indicate that the threshold of efferent neurons to JSCPs is very sensitive to excitatory and inhibitory synaptic inputs. Iontophoretic applications of gamma-aminobutyric acid (GABA) increased the threshold to JSCPs, and glutamate reduced the threshold. Electrical stimulation of afferent pathways at intensities just below threshold for eliciting action potentials resulted in a dramatic decrease in JSCP threshold. This initial short-latency threshold decrease was specific to stimulation of particular afferent pathways and is thought to reflect excitability changes associated with EPSPs. Examination of such subliminal responses revealed subthreshold synaptic inputs that were not revealed by examination of all-or-none action potentials. In contrast to the specificity of the short-latency threshold decrease, a long-lasting increase in JSCP threshold was seen in virtually all neurons after stimulation of each of the afferent pathways tested. This increase in threshold usually began 20-40 ms after stimulation, lasted for 100-200 ms, and is thought to reflect excitability changes associated with a long-lasting inhibitory postsynaptic potential (IPSP) seen in many cortical neurons. 4. Many neurons in primary somatosensory cortex of rat, cat, and rabbit have no demonstrable receptive fields.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗
PubMed1991

Efferent neurons and suspected interneurons in second somatosensory cortex of the awake rabbit: receptive fields and axonal properties.

1. Receptive-field properties of antidromically identified efferent neurons within the representation of vibrissae and sinus hairs above the mouth were examined in secondary somatosensory cortex (S-2) of fully awake adult rabbits. Efferent neurons studied included callosal neurons (CC neurons, n = 88), ipsilateral corticocortical neurons (C-IC neurons, n = 51) that project to primary somatosensory cortex (S-1), and corticofugal neurons of layer 5 (CF-5 neurons, n = 63) and layer 6 (CF-6 neurons, n = 42) that project to and/or beyond the thalamus. Appropriate collision tests demonstrated that substantial numbers of corticocortical efferent neurons (21 of 113 tested) project an axon to both the corpus callosum and to ipsilateral S-1. 2. Suspected interneurons (SINs, n = 62) were also studied. These neurons were not activated antidromically from any stimulus site but did respond synaptically to electrical stimulation of the ventrobasal (VB) thalamus with a burst of three or more spikes at frequencies of 600 to greater than 900 Hz. Most of these neurons also responded synaptically to stimulation of S-1 and the corpus callosum. The action potentials of these neurons were much shorter (mean, 0.49 ms) than those of efferent neurons (mean, 1.01 ms). 3. CF-5 neurons differed from CC, C-IC, and CF-6 neurons in their spontaneous firing rates, axonal properties, and receptive-field properties. Whereas CF-5 neurons had a mean spontaneous firing rate of 5.7 spikes/s, CC, C-IC, and CF-6 neurons all had mean values of less than 1/s. Axonal conduction velocities of CF-5 neurons were much higher (mean, 11.90 m/s) than either CC (mean, 2.63 m/s), C-IC (mean, 0.86 m/s), or CF-6 (mean, 1.73 m/s) neurons. A decrease in antidromic latency (the "supernormal" period), which was dependent on prior impulse activity, was seen in most CC, C-IC, and CF-6 neurons but was minimal or absent in CF-5 neurons of comparable conduction velocity. Although all CF-5 neurons responded to peripheral sensory stimulation, many CC (52%), C-IC (49%), and CF-6 (55%) neurons did not. CC and CF-6 neurons that did not respond to sensory stimulation had significantly lower axonal conduction velocities and spontaneous firing rates than those that responded to such stimulation. Whereas no CC, C-IC, or CF-6 neuron responded synaptically to callosal stimulation, 43% of CF-5 neurons (and 78% of SINs) did so respond. Similar differences in synaptic responsivity to stimulation of S-1 were seen in these populations.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗
PubMed1990

Efferent neurons and suspected interneurons in S-1 forelimb representation of the awake rabbit: receptive fields and axonal properties.

1. Receptive-field properties of antidromically identified efferent neurons within the cutaneous forelimb representation of primary somatosensory cortex (S-1) were examined in fully awake rabbits. Efferent neurons studied included callosal neurons (CC neurons, n = 52), ipsilateral corticocortical neurons (C-IC neurons, n = 48) that project to or beyond the second somatosensory cortical area (S-2), and corticofugal neurons of layer 5 (CF-5 neurons, n = 97) and layer 6 (CF-6 neurons, n = 59) that project to and/or beyond the thalamus. 2. An additional class of neurons was studied that was not activated antidromically from any stimulus site, but which responded synaptically to electrical stimulation of the ventrobasal (VB) thalamus with a burst of three or more spikes at frequencies of 600 to greater than 900 Hz. Most of these neurons also responded synaptically to stimulation of S-2 and the corpus callosum. The action potentials of these neurons were much shorter (mean = 0.45 ms) than those of efferent neurons (mean = 0.95 ms). Such properties have been associated with interneurons found throughout the central nervous system, and these neurons are thereby referred to as suspected interneurons (SINs). 3. CF-5 neurons differed from CC, C-IC, and CF-6 neurons in their spontaneous firing rates, axonal properties, and receptive-field properties. Whereas CF-5 neurons had a mean spontaneous firing rate of 5.5 spikes/s, CC, C-IC, and CF-6 neurons had mean values of less than 1/s. Axonal conduction velocities of CF-5 neurons were much higher (mean = 12.92 m/s) than either CC (mean = 2.15 m/s), C-IC (mean = 1.31 m/s), or CF-6 (mean = 2.53 m/s) neurons. A decrease in antidromic latency (the "supernormal" period) that was dependent on prior impulse activity was seen in the great majority of CC, C-IC, and CF-6 neurons but was either minimal or absent in CF-5 neurons of comparable conduction velocity. A higher proportion of CF-5 neurons (98%) responded to peripheral sensory stimulation than did either CC (75%), C-IC (71%), or CF-6 (51%) neurons. CF-6 and C-IC neurons that did not respond to sensory stimulation had significantly lower axonal conduction velocities and spontaneous firing rates than those that responded to such stimulation. 4. Cutaneous receptive fields were seen in most neurons that could be driven by peripheral stimulation.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1989

Efferent neurons and suspected interneurons in S-1 vibrissa cortex of the awake rabbit: receptive fields and axonal properties.

1. The behavioral tractability of the rabbit was exploited and enabled, in the fully awake state, receptive-field analysis of antidromically identified efferent neurons within the vibrissa representation of primary somatosensory cortex (S-1). Efferent neurons studied included ipsilateral corticocortical neurons (C-IC neurons, n = 56) that project to or beyond the second somatosensory cortical area (S-2) and corticofugal neurons of layer 5 (CF-5 neurons, n = 75) and layer 6 (CF-6 neurons, n = 92) that project to and/or beyond the thalamus. 2. An additional class of neurons was studied that was not activated antidromically from any stimulus site, but which responded synaptically to electrical stimulation of the ventrobasal (VB) thalamus with a burst of three or more spikes at frequencies of 600 to greater than 900 Hz. Most of these neurons also responded synaptically to stimulation of S-2. The action potentials of these neurons were much shorter (mean = 0.43 ms), than those of efferent neurons (mean = 0.98 ms). Such properties have been associated with interneurons found throughout the central nervous system, and these neurons are thereby referred to as suspected interneurons (SINs). Although SINs were found at all cortical depths, a strong peak in the distribution occurred just superficial to the peak in the distribution of CF-5 neurons. Most SINs located within this peak responded to deflection of only a single vibrissa. In contrast, SINs located in layer 6 and in layer 2-3 responded to deflection of many vibrissae (median = 11.0 and 5.5 vibrissae, respectively). In addition, SINs of layer 6 and layer 2-3 had significantly longer synaptic latencies to stimulation of VB thalamus than did SINs located at intermediate cortical depths. 3. The properties of efferent neurons and SINs differed considerably. Efferent neurons never responded to stimulation of VB thalamus with the high-frequency burst of spikes characteristic of SINs. Although greater than 70% of CF-6, CF-5 and C-IC neurons had receptive fields that were directionally selective, only 20% of SINs showed any degree of directional selectivity. Furthermore, SINs showed both much lower angular thresholds to vibrissa deflection and a much greater ability to follow high-stimulus frequencies than was seen in efferent neurons. The spontaneous firing rates of SINs had a mean value of 16.5 spikes/s, which was the highest seen in any population within S-1. 4. CF-5 neurons had a number of properties which contrasted with those of both CF-6 and C-IC neurons.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1988

Neuronal responses in rabbit cingulate cortex linked to quick-phase eye movements during nystagmus.

1. Responses of single units in area 29 of cingulate cortex were examined in alert rabbits during vestibular and optokinetic nystagmus. Eye movements were measured by optically detecting the position of an infrared light-emitting diode attached to the cornea. 2. Fourteen percent of cingulate cells (68 of 477 isolated units) had responses that were correlated to the occurrence of quick phases. Latencies ranged from 60 ms before to 220 ms after the onset of the quick phase with a mean of 70 ms and standard deviation of 58 ms. Most units responded during or following quick phases, although four units had responses that preceded the quick-phase onset. 3. Unitary responses during quick phases were not due to visual field movement, since these responses occurred in the dark as well as the light. The responses were not dependent upon vestibular stimulation, since responses related to spontaneous saccadelike eye movements were observed in cingulate quick-phase neurons. 4. The majority (37 of 52) of the quick-phase neurons had a directional preference. Approximately equal numbers of directional units responded to quick phases directed ipsilaterally and contralaterally with respect to the recording site. 5. About one-fourth of the quick-phase units were bidirectional (15 of 52) with virtually equal responses to ipsilaterally and contralaterally directed quick phases. 6. Auditory and/or somatosensory responses were observed in only five of the quick-phase cells. All such multimodal units were bidirectional. 7. The quick-phase units were histologically confirmed to be primarily in area 29d of cingulate cortex. Although most cells were located in layer V, some were isolated in layer II-III. 8. Cingulate cortex has reciprocal connections with visual cortex and oculomotor-related thalamic nuclei and projects to the layers of the superior colliculus that are involved in oculomotor control. Responses to quick phases in cingulate neurons may synchronize cingulate cortex responsiveness with the arrival of new, and potentially significant, visual information.

Animals↗
PubMed1988

Efferent neurons and suspected interneurons in binocular visual cortex of the awake rabbit: receptive fields and binocular properties.

1. In fully awake rabbits the stability of the two eyes was monitored and was sufficient to enable receptive-field analysis of antidromically identified efferent neurons and suspected interneurons in the binocular segment of visual area 1. Efferent neurons analyzed included callosal efferent neurons (CC neurons, n = 52), neurons projecting to visual area 2 (CV2 neurons, n = 35), corticotectal neurons (CT neurons, n = 43), and corticogeniculate neurons (CG neurons, n = 51). Six additional neurons projected a branching axon to both the corpus callosum and visual area 2. 2. Most CC and CV2 neurons were found in layer 2-3 and had receptive fields of the simple type. Only two corticocortical neurons with complex receptive fields were found. Orientation tuning ranges of CC and CV2 simple cells were similar and end stopping was prevalent in both CC (62%) and CV2 (45%) neurons. Axonal conduction velocities of CC and CV2 neurons were low (mean = 3.5 and 1.4 m/s, respectively) and visually nonresponsive CC neurons (19%) had conduction velocities that were significantly lower than visually responsive neurons. Spontaneous firing rates of corticocortical neurons were low (mean less than 1 spike/s) and these neurons responded to a lower range of stimulus velocities than did corticofugal neurons. 3. Most CG neurons had simple receptive fields and none had a complex field. Orientation tuning ranges of these neurons were comparable to those of CC and CV2 neurons, but a significantly smaller proportion (12%) were end stopped. Both spontaneous firing rates (mean = less than 1 spike/s) and axonal conduction velocities (mean = 2.4 m/s) of CG neurons were low and, as was found for CC neurons, visually nonresponsive CG neurons (25%) had significantly lower conduction velocities than did visually responsive neurons. 4. CT neurons had receptive fields that were predominantly complex (37%), motion/uniform (28%), or simple (26%). Conduction velocities (mean = 10.9 m/s) and spontaneous firing rates (mean = 7 spikes/s) of CT neurons of all receptive-field types were much higher than those of CC, CV2, and CG neurons. 5. An additional class of neurons was studied that responded synaptically at a short latency to electrical stimulation of the dorsal lateral geniculate nucleus (LGNd) with a burst of three or more spikes at frequencies of 600-900 Hz. These neurons showed a high degree of synaptic convergence, also responding synaptically with a high-frequency burst of spikes to stimulation of both visual area 2 and the corpus callosum.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1987

Corticogeniculate neurons, corticotectal neurons, and suspected interneurons in visual cortex of awake rabbits: receptive-field properties, axonal properties, and effects of EEG arousal.

The intrinsic stability of the rabbit eye was exploited to enable receptive-field analysis of antidromically identified corticotectal (CT) neurons (n = 101) and corticogeniculate (CG) neurons (n = 124) in visual area I of awake rabbits. Eye position was monitored to within 1/5 degrees. We also studied the receptive-field properties of neurons synaptically activated via electrical stimulation of the dorsal lateral geniculate nucleus (LGNd). Whereas most CT neurons had either complex (59%) or motion/uniform (15%) receptive fields, we also found CT neurons with simple (9%) and concentric (4%) receptive fields. Most complex CT cells were broadly tuned to both stimulus orientation and velocity, but only 41% of these cells were directionally selective. We could elicit no visual responses from 6% of CT cells, and these cells had significantly lower conduction velocities than visually responsive CT cells. The median spontaneous firing rates for all classes of CT neurons were 4-8 spikes/s. CG neurons had primarily simple (60%) and concentric (9%) receptive fields, and none of these cells had complex receptive fields. CG simple cells were more narrowly tuned to both stimulus orientation and velocity than were complex CT cells, and most (85%) were directionally selective. Axonal conduction velocities of CG neurons (mean = 1.2 m/s) were much lower than those of CT neurons (mean = 6.4 m/s), and CG neurons that were visually unresponsive (23%) had lower axonal conduction velocities than did visually responsive CG neurons. Some visually unresponsive CG neurons (14%) responded with saccadic eye movements. The median spontaneous firing rates for all classes of CG neurons were less than 1 spike/s. All neurons synaptically activated via LGNd stimulation at latencies of less than 2.0 ms had receptive fields that were not orientation selective (89% motion/uniform, 11% concentric), whereas most cells with orientation-selective receptive fields had considerably longer synaptic latencies. Most short-latency motion/uniform neurons responded to electrical stimulation of the LGNd (and visual area II) with a high-frequency burst (500-900 Hz) of three or more spikes. Action potentials of these neurons were of short duration, thresholds of synaptic activation were low, and spontaneous firing rates were the highest seen in rabbit visual cortex. These properties are similar to those reported for interneurons in several regions in mammalian central nervous system. Nonvisual sensory stimuli that resulted in electroencephalographic arousal (hippocampal theta activity) had a profound effect on the visual responses of many visual cortical neurons.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1986

Thalamic inputs to visual areas 1 and 2 in the rabbit.

Thalamic projections to two cortical representations of the visual field, visual areas 1 and 2 (V1, V2), in the rabbit were studied by using the retrograde transport of horseradish peroxidase (HRP). Physiological guidance was employed to inject small amounts of HRP into topographically defined regions of V1 or V2. Injections restricted to V1 revealed a dense projection from the dorsal lateral geniculate nucleus as well as projections from the pulvinar, the posterior thalamic nucleus, and the ventral lateral nucleus. Injections restricted to V2 revealed projections from the pulvinar, the ventral lateral nucleus, and the posterior thalamic nucleus, but only a slight projection from the dorsal lateral geniculate nucleus. V2, but not V1, receives an input from neurons within the fiber plexus between the dorsal lateral geniculate nucleus and the pulvinar. Finally, the neurons in the lateral geniculate nucleus that project to V2 have larger somata on average than those that project to V1 (means = 18.25 micron vs. 14.04 micron, P less than .001).

Animals↗
PubMed1986

Rabbit cingulate cortex: cytoarchitecture, physiological border with visual cortex, and afferent cortical connections of visual, motor, postsubicular, and intracingulate origin.

The connections of cingulate cortex with visual, motor, and parahippocampal cortices in the rabbit brain are evaluated by using a modified Brodmann cytoarchitectural scheme, electrophysiological mapping techniques, and the pathway tracers horseradish peroxidase (HRP) and tritiated amino acids. Rabbit cingulate cortex can be divided into areas 25, 24, and 29. Area 29 is of particular interest because area 29d has a lateral extension with a granular layer IV, area 29b has a caudal extension in which the connections differ from anterior area 29b, and there is a prominent area 29e. Cytoarchitectural delineation of the lateral border of area 29d with area 17 closely approximates the medial edge of the visual field representation in area 17 as determined electrophysiologically. The main interconnections between visual and cingulate cortices occur between cingulate areas 24b and 29d and visual areas 18 and medial parts of area 17. Projections between areas 29d and 18 are organized in a loose topographic fashion with rostral parts of each and caudal parts of each being reciprocally connected. Neurons mainly in superficial layer II-III of areas 17 and 18 project to layer I of area 29d, while the reciprocal projection originates from neurons in layer V of area 29d and project mainly to layer I of areas 17 and 18. The medial portion of motor area 8 projects to areas 18 and 29d and has a smaller projection to area 17. Postsubicular area 48 is reciprocally connected with area 29d, and it also projects to areas 29b and c. The subiculum projects to areas 29a and 29c but only to the anterior two-thirds of area 29b not the posterior one-third. Rostral area 29d receives the most extensive intrinsic cingulate projections including those from all major cytoarchitectural divisions. Interconnections between areas 29d and 29b appear to be topographically organized in the rostrocaudal plane. Area 29c projects more heavily to area 29b than vice versa. Finally area 29d projects mainly to area 24b in anterior cingulate cortex. In conclusion, rostral area 29d has extensive connections with visual areas 17 and 18, motor area 8, and all subdivisions of cingulate cortex. In light of these connections, it may play a pivotal role in associative functions of the rabbit cerebral cortex including visuomotor integration.

Animals↗
PubMed1985

Receptive-field and axonal properties of neurons in the dorsal lateral geniculate nucleus of awake unparalyzed rabbits.

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)

Animals↗
PubMed1979

Dependence of refractory period measurements on conduction distance: a computer simulation analysis.

Computer simulations were used to study the recovery of conduction velocity in the temporal and spatial domains during the relative refractory period. The impulse exhibits increased duration and reduced amplitude during the relative refractory period as well as a reduced conduction velocity. Changes in conduction velocity are reflected by a deviation from linearity in the plots of latency variation versus interstimulus interval and of interval-between-impulses versus intersimulus interval. The latency increase for the second impulse is monotonically related to interstimulus interval, and is maximal at the beginning of relative refractory period. The magnitude of the latency increase is also related monotonically, but not in a linear manner, to conduction distance. The distance-dependence of latency variation during the relative refractory period is most marked close to the site of impulse initiation. These findings may be relevant to relative refractory period measurements in clinical neurophysiology.

Action Potentials↗
PubMed1978

Characteristics of interhemispheric impulse conduction between prelunate gyri of the rhesus monkey.

Cells of origin of the corpus callosum (callosal efferent neurons) in prelunate gyrus (area OA) of the rhesus monkey were studied using electrophysiological techniques. Monkeys were chronically prepared and callosal efferent neurons were identified by their antidromic activation following electrical stimulation of the contralateral prelunate gyrus and/or the splenium of the corpus callosum. Interhemispheric antidromic latencies ranged from 2.6--18.0 ms (median = 7.0 ms) while the conduction velocity along the length of the axon ranged from 2.8 to 22.5 M/s (median = 7.4 M/s) while the conduction velocity along the length of the axon ranged from 2.8 to 22.5 M/s (median = 7.4 M/s. Following the relative refractory period of a single prior impulse, all but one of 61 callosal efferent neurons studied showed a supernormal period of increased axonal conduction velocity and excitability. Following several prior impulses, the supernormal period was followed by a subnormal period of decreased axonal conduction velocity and excitability, which, depending on the number of prior impulses, lasted from several hundred ms to nearly 2 min.

Animals↗
PubMed1978

Intensity coding in primate visual system.

The pupil reflex and the discharge of LGN cells of the awake macaque were measured under stimulus conditions that yielded evidence for wide-range intensity coding in human psychophysical experiments. Ganzfeld flashes of white light were delivered under dark-adapted conditions to the surgically immobilized eye of the monkey while the other eye was observed in the infrared. Three-sec flashes elicited a consensual pupil reflex that was graded from -8 to 0 log Lamberts (L), indicating that the optic nerve fibers are capable of coding at least an 8 log-unit range of light intensity. In the physiological experiments, shorter flashes (0.1-0.5 sec) but otherwise identical conditions elicited monotonically graded responses from one type of LGN cell over the photopic range of -5 to 0 log L. Responses from other types of LGN cells were also graded over wide ranges but had different thresholds and, in some cases, nonmonotonic intensity-response functions. Latency of the excitatory LGN responses decreased with increasing intensity according to a power function with slope of-0.08. The pupil reflex and the LGN cell excitatory responses approximate power functions of light intensity with exponents of 0.22 and 0.14-0.29 respectively. The range of intensity coding found for single LGN cells is the widest yet reported for diffuse stimuli.

Animals↗
PubMed1978

Evaluation of a surgical method for immobilizing the eye of an alert monkey.

One eye of a macaque monkey was immobilized by severing the third, fourth, and sixth cranial nerves. The residual movements of the operated eye were measured by repeatedly mapping the position of a visual receptive field. Movements of several degrees were caused by contraction of the orbital musculature during the closure blink. The amount of movement was dramatically reduced by paralysis of the superficial orbital muscles with a local anesthetic. Side effects of surgical immobilization include increased risk of corneal clouding and eye infection. In one monkey intraocular pressure was lowered for several weeks. Regeneration of the severed nerves causes return of some voluntary movement of the eye, which is not coordinated with movements of the unoperated eye even after nine months postoperative survival. The suitability of this approach for studies on the visual nervous system is discussed.

Abducens Nerve↗