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Biomedical subjects

A F Fuchs

Publications and source records attributed to A F Fuchs.

At least 91 records · Page 5Linked to original sources
PubMed1979

Spatial and temporal properties of X and Y cells in the cat lateral geniculate nucleus.

1. Extracellular recordings were obtained from units in the dorsal lateral geniculate nucleus of anaesthetized cats. 2. Of sixty-nine units, sixty-three could be unambiguously identified as either X (n = 33) or Y (n = 30) by testing the presence of a null response to stationary sine wave gratings presented in different spatial phases. 3. In response to stationary gratings flashed on and off, Y cells exhibited bigger, more transient responses than X cells. 4. All Y cells but few X cells exhibited a shift effect (modulated periphery effect). 5. In response to drifting sine wave gratings of different spatial frequencies, X cells preferred higher spatial frequencies and showed smaller peak contrast sensitivities and somewhat narrower tuning curves than Y cells. 6. In response to a sine wave grafting of optimal spatial frequency drifting at different velocities, X and Y cells had similar temporal tuning curves. However, Y cells, largely because they preferred lower spatial frequencies, preferred higher drift velocities than X cells. 7. Our data suggest that X and Y cells can be differentiated objectively on the basis of a number of discharge parameters. These parameters are compared with similar data collected by others from neurones in the visual cortex.

Action Potentials↗
PubMed1978

Saccadic, smooth pursuit, and optokinetic eye movements of the trained cat.

1. Cats were trained to track a small target by rewarding them for keeping their eyes on target. Eye movements were measured by the electromagnetic search coil technique. 2. Cat saccades are qualitatively similar to primate saccades, but exhibit more variability in their parameters. However, they have longer durations and lower maximum velocities than primate saccades. As in the monkey, the duration of the horizontal or vertical component of an oblique saccade is lengthened when the orthogonal component has a larger amplitude. Cat saccades can be modified in midflight like human saccades. Opening the visual feed-back loop by controlling target position with eye position causes the cat to execute a staircase of equal amplitude saccades if a retinal error is present. Increasing the amount of visual feed-back induces saccadic oscillations. 3. Horizontal smooth pursuit of a 0 . 5 deg visual target is limited to velocities of less than 1 deg/sec. However, moving an optokinetic background with the 0 . 5 deg target enables the cat to achieve higher horizontal smooth eye velocities of up to 8 . 5 deg/sec. Prolonged (10-20 sec) constant velocity rotation of an optokinetic drum evokes horizontal slow-phase velocities of up to 28 deg/sec. In response to vertical movements of the target and optokinetic background, smooth eye movements reached 6 deg/sec maximum upward velocities but only 2 . 5 deg/sec maximum downward velocities. Opening the feed back loop with no retinal error present causes the eye to exhibit a growing smooth trajectory. The response to a Rashbass step-ramp target suggests that the feline smooth response is a function of target movement rather than displacement. 4. These data suggest that cat saccadic eye movements resemble those of primates while the cat smooth pursuit and optokinetically induced eye movements are more similar to those of the rabbit.

Animals↗
PubMed1978

Role of primate flocculus during rapid behavioral modification of vestibuloocular reflex. I. Purkinje cell activity during visually guided horizontal smooth-pursuit eye movements and passive head rotation.

1. Extracellular recordings were obtained from 124 Purkinje cells (P-cells) in the flocculus of alert monkeys. P-cell simple spike-firing rate was analyzed quantitatively during various combinations of smooth-pursuit eye movement and passive head rotation. 2. During sinusoidal smooth eye movements, 80% of the P-cells displayed increased firing rate during ipsilateral and 20% during contralateral eye movement. Over the frequency range 0.3--1.4 Hz, firing-rate modulation was proportional to and in phase with maximum eye velocity. During the steady state of triangle-wave tracking, firing rate increased monotonically as a function of eye velocity. Since firing rate was uncorrelated with retinal-error velocity, one component of P-cell firing rate was related to eye velocity. 3. During the transient phase of triangle-wave tracking, when an instantaneous change in the direction of target movement caused a large retinal-error velocity, 40% of the P-cells were related only to eye velocity. Sixty percent of the P-cells displayed an overshoot or undershoot in firing rate, indicating a relationship to either retinal-error velocity or eye acceleration as well as to eye velocity. 4. During the vestibuloocular reflex (VOR), evoked by head rotation in the dark, P-cell firing rate was only weakly modulated. In contrast, when the monkey suppressed the VOR by fixating a target that rotated with him, P-cell rate was deeply modulated. Since the modulation was proportional to and in phase with maximum head velocity, another component of P-cell firing rate was related to head velocity. 5. Of 36 P-cells tested, 35 displayed firing-rate modulation during both suppression of the VOR and smooth-pursuit eye movement. P-cells that reached peak firing rate during ipsilateral head rotation also reached peak firing rate during ipsilateral smooth eye rotation. Average population sensitivitites to head velocity and eye velocity were equal. In three conditions in which eye and head velocity were elicited simultaneously, P-cell firing rate could be predicted by the linear, vector addition of the separate eye and head velocity components of firing rate. Therefore, the relatively weak modulation of P-cell firing rate during the VOR in the dark can be accounted for by the cancellation of equal but opposite head and eye velocity components. 6. The connections of flocculus P-cells to interneurons in the brain stem VOR pathways have been established in other mammals. In the context of those connections, P-cell firing patterns were appropriate to facilitate the eye movements the monkey was required to make. We conclude that the flocculus is important for sustaining any smooth eye movements that are different from those evoked by head rotation in the dark. The eye velocity component may represent an efference copy signal that sustains ongoing eye velocity during smooth pursuit.

Animals↗
PubMed1978

Role of primate flocculus during rapid behavioral modification of vestibuloocular reflex. II. Mossy fiber firing patterns during horizontal head rotation and eye movement.

1. Extracellular recordings were obtained from 113 mossu fibers (MFs) in the flocculus of alert monkeys trained to perform a visual tracking task during sinusoidal, horizontal head rotation. The analysis of MF discharge patterns was designed to allow quantitative comparison of the discharge properties of flocculus MFs with brain stem cell populations from which the MFs might originate and with flocculus Purkinje cells (P-cells). Based on their firing patterns, MFs were divided into two classes. Vestibular MFs discharged in relation to head velocity and, in some cases, also in relation to eye movement. Eye movement MFs discharged only in relation to one or more components of eye movement. 2. Vestibular MFs were subdivided into three classes. Vestibular-only MFs (n = 15) displayed a modulation in firing rate during head rotation but exhibited no relationship to spontaneous eye movements. Vestibular-plus-saccade MFs (n = 14) displayed a modulation in firing rate during head rotation that quantitatively resembled the modulation in vestibular-only MFs. In addition, a pause in firing rate interrupted the vestibular modulation during saccades in one or more directions. Vestibular-plus-position MFs (n = 4) exhibited steady firing rates that were linearly related to horizontal eye position in the absence of vestibular stimulation. Sinusoidal head rotation evoked a modulation ofiring rate above and below the firing rate set by the eye position. 3. during sinusoidal head rotation, vestibular MF firing rate led head velocity by an average of 24 degrees. The amplitude of MF firing-rate modulation increased as a function of the frequency of head rotation and, hence, maximum head velocity. Since these characteristics are similar to those displayed by P-cells during suppression of the VOR, vestibular MFs probably transmit the head velocity component of P-cell firing rate to the flocculus. Based on evidence from other mammals and a quantitative comparison of population discharge characteristics, it is likely that vestibular MFs originate from the vestibular nerve and from cells in the medial vestibular nucleus. 4. Based on their discharge patterns, eye movement MFs were also subdivided into three classes. Burst MFs (n = 14) emitted a high-frequency burst of spikes prior to and during saccades in one or more direction, but were silent during steady fixation. Burst-tonic MFs (n = 53) emitted a burst of spikes prior to saccades in a preferred ("on") direction, ceased firing during saccades in the opposite ("off") direction, and exhibited steady firing rates that increased as steady gaze shifted in the on direction. Tonic MFs (n = 13) displayed steady firing rates that increased as the position of steady gaze shifted in the on direction, and either paused or exhibited step changes in firing rate during saccades. 5. During steady fixation, 64% of tonic and burst-tonic MFs were recruited into maintained firing within +/- 10 degrees of the primary direction of gaze...

Animals↗
PubMed1977

Discharge properties of neurons in the monkey thalamus tested with angular acceleration, eye movement and visual stimuli.

Monkeys were trained to make visually evoked eye movements while undergoing simultaneous head rotation. Single units were recorded in the pregeniculate nucleus (PGN). PGN neurons discharged during each saccade, but there was no change in activity with horizontal head acceleration or with various combinations of head and smooth pursuit eye movements as previously described in the cat. Therefore, the anatomical homology between LGNv and PGN does not appear to have a neurophysiological basis. Neurons in the oral part of VPL or occasionally in VPI discharged as a function of head velocity but not with saccades, smooth pursuit or fixation eye movements, nor after brief light flashes or during smooth pursuit across structured backgrounds. This suggests that VPLo and VPI are only vestibular relay nuclei and not concerned with vestibular/visual or vestibular/oculomotor interactions.

Animals↗
PubMed1977

Bilateral lesions of the medial longitudinal fasciculus in monkeys: effects on the horizontal and vertical components of voluntary and vestibular induced eye movements.

Bilateral transections across the brainstem interrupted the medial longitudinal fasciculus (MLF) in three monkeys trained to make eye movements while subjected to horizontal or vertical angular accelerations. Eye movements measured before and after the lesion revealed deficits in both voluntary and vestibular compensatory eye movements; the deficits differed in the horizontal and vertical directions. Vertical saccades in both directions were normal but eccentric positions of fixation could not be maintained; a drift toward the midline followed by a corrective saccade produced vertical fixation nystagmus. Furthermore, the vertical vestibulo-ocular reflex (VOR) was abolished and vertical smooth pursuit was impaired. Along the horizontal meridian, adduction across the midline could not be achieved during either saccades, smooth pursuit, or the VOR. Temporal saccades were normal whereas nasal saccades were considerably slowed. If the eye was not required to cross the midline, the phase shift during the VOR was within 15 deg of normal in each eye. The gain of the VOR was reduced to about 0.4 immediately after the lesion, but recovered within one month. These findings suggest that the MLF transmits quite different kinds of information to horizontal and vertical oculomotoneurons and that deficits in vertical eye movements may be a sensitive indicator of anterior internuclear ophthalmoplegia.

Animals↗
PubMed1976

Responses of fibers in medial longitudinal fasciculus (MLF) of alert monkeys during horizontal and vertical conjugate eye movements evoked by vestibular or visual stimuli.

Extracellular recordings were obtained from 37 histologically identified MLF fibers near the trochlear nucleus in alert monkeys trained to perform a visual tracking task and subjected to adequate horizontal and vertical vestibular stimulation. The behavioral paradigm permitted independent quantitative assessment of a fiber's response to eye or head movements. 2. According to their discharge pattern, almost all MLF fibers were placed in one of two classes: 1) Horizontal burst-tonic fibers (n = 20). During both vestibular and visually evoked eye movements, burst-tonic fibers discharged in strict relation to horizontal eye movements, exhibiting a burst of activity prior to on-direction saccades and steady firing related to horizontal eye position during fixations. 2) Vertical vestibular plus eye-position fibers (n = 14). Vertical fibers discharged in relation to vertical head velocity in the absence of eye movements and in relation to vertical eye position in the absence of head movement, and paused with saccades in any direction. 3. The quantitative similarity of horizontal burst-tonic fiber discharge to that of ipsilateral medial rectus oculomotoneurons suggests that burst-tonic fibers provide the major excitatory synaptic drive to medial rectus motoneurons during conjugate eye movements of vestibular or visual origin. 4. The discharge pattern of vertical vestibular plus eye-position fibers is significantly different from that of oculomotoneurons, suggesting that additional neural processing of vertical fiber information must occur in the mesencephalon. 5. The functional dichotomy of horizontal and vertical MLF fibers and their contrasting discharge patterns provide new evidence for the anatomic and functional separation of horizontal and vertical eye movement mechanisms in the pons and mesencephalon, respectively.

Action Potentials↗
PubMed1975

Monkey retinal ganglion cells: morphometric analysis and tracing of axonal projections, with a consideration of the peroxidase technique.

This paper presents evidence on the retinal distribution and central projections of retinal ganglion cells of various cell body sizes in the adult macaque monkey. The ganglion cell sizes have been determined by computer assisted measurement of camera lucida drawings at various eccentricities of both flat mounted and sectioned retinae. The pattern of projections of individual ganglion cells to the dorsal lateral geniculate nucleus and superior colliculus has been studied using retrograde axonal transport of horseradish peroxidase. Following peroxidase injections into the parvocellular laminae of the geniculate, virtually every ganglion cell was labeled within a circumscribed zone of the retina known to project to the region of the geniculate immediately surrounding the injection needle tip. After magnocellular injections, only the largest cells of the peripheral retina and approximately 26% of the ganglion cells of the parafovea were labeled. Peroxidase injections into the superior colliculus produced labeling of scattered ganglion cells of all sizes in the retina, although no labeled cells were found within the centralmost 10 degrees eccentricity. From these observations it is concluded that all ganglion cells of the macaque retina project to the parvocellular layers of the dorsal lateral geniculate, but that only the largest ganglion cells of the more peripheral retina and not all cells of the parafovea project to the magnocellular laminae. In contrast, only scattered ganglion cells, although these are of all sizes, appear to project to the superior colliculus. Two major problems with the peroxidase tracing technique are described: 1. The extent of stainable peroxidase activity around the injection site appears to be larger than the area of injected tracer actually available for uptake by axons to produce labeled cells. 2. Cut or damaged axons appear to incorporate peroxidase sufficiently to produce labeling of the cell body.

Animals↗
PubMed1975

The origin of efferent pathways from the primary visual cortex, area 17, of the macaque monkey as shown by retrograde transport of horseradish peroxidase.

The retrograde transport of horseradish peroxidase has been used to identify efferent cells in area 17 of the macaque. Cells projecting to the lateral geniculate nucleus are small to medium sized pyramidal neurons with somata in lamina 6 and the adjacent white matter. The projection to the parvocellular division arises preferentially from the upper half of lamina 6, while that to the magnocellular division arises preferentially from the lower part of the lamina. The projection to both superior colliculus and inferior pulvinar arises from all sizes of pyramidal neurons lying in lamina 58 (Lund and Boothe, '75); at least pyramidal neurons of lamina 5B send collateral axon branches to both destinations. Injections with extensive spread of horseradish peroxidase show that many cells of lamina 4B and the large pyramidal neurons of upper lamina 6 also project extrinsically but their terminal sites have not been identified. Other studies have indicated that cells of laminae 2 and 3 project to areas 18 and 19. Therefore every lamina of the visual cortex, with the exception of those receiving a direct thalamic input, contains cells projecting extrinsically. Further, each lamina projects to a different destination and from Golgi studies can be shown to contain cells with specific patterns of dendritic branching which relate to the distribution of thalamic afferents and to the patterns of intracortical connections. These findings emphasise the significance of the horizontal organisation of the cortex with relation to the flow of information through it and contrast with the current concept of columnar organisation shown in physiological studies.

Animals↗
PubMed1975

Single-unit responses to natural vestibular stimuli and eye movements in deep cerebellar nuclei of the alert rhesus monkey.

To study the possible role of the cerebellum in the vestibular-ocular reflex, extracellular responses of cerebellar nuclear neurons were recorded in awake monkeys during natural vestibular stimulation; 115 neurons in the fastigial nucleus responded to horizontal sinusoidal accelerations applied to the head by means of whole-body rotation. More than 75% of these cells were located in a distinct layer, 500 mum thick, in the rostral part of the fastigial nucleus; they were excited by contralateral horizontal angular acceleration and inhibited by ipsilateral rotation (type IIf neurons). The remaining 25% of the population were scattered more caudally in the nucleus, and were excited by ipsilateral rotation and inhibited by contralateral rotation (type If). All showed fairly high resting discharges, averaging 50 spikes/s. Sinusoidal horizontal rotation (0.2--4.8 HZ) produced clear periodic modulation of the firing rate of fastigial neurons, which was approximately sinusoidal about the resting rate at low frequencies. As the frequency of oscillation (and the applied acceleration) increased, the sinusoidal modulation of unit firing increased in amplitude; at high stimulus frequencies the firing rate was usually driven to zero during the inhibitory part of stimulus cycle, but did not saturate in the excitatory half leading to an increase in the mean firing rate. The maximum firing rates of fastigial neurons were related to the peak acceleration by a power function. At all stimulus frequencies, the peak firing frequency of fastigial neurons lagged the input angular acceleration. Maximum firing of most units occurred just prior to the maximum velocity of the head. The gain and phase lag of the averaged unit discharge relative to head acceleration were calculated by Fourier analysis, using the fundamental as a first approximation of the response. Over a 20-fold stimulus range (0.2--4.0 HZ), mean phage lags of type IIf unit responses with respect to the applied acceleration remained relatively constant; the phase lag at 0.9 HZ measured 62 plus or minus 13 degrees. This phase lag is very similar to that recorded from vestibular nerve fibers (15), suggesting that type IIf fastigial neurons provide an excitatory signal to the ipsilateral vestibular nuclei which is in phase with direct vestibular afferent input, although functionally opposite in sign. Over the same frequency range, the gain decreased at minus- 18 dB/decade. Our data suggests that the majority of fastigial neurons work in parallel with flocculus Purkinje cells to functionally inhibit type Iv neurons in the ipsilateral vestibular nuclei.

Acceleration↗
PubMed1975

Unit activity in vestibular nucleus of the alert monkey during horizontal angular acceleration and eye movement.

Single units were recorded from the vestibular nuclei of unanesthetized monkeys that were rotated in the horizontal plane while simultaneously pressing individual buttons in a controlled array which turned with hem. Using this behavioral paradigm, it was possible to 1) determine the relationship of unit discharge to eye movements measured by the DC-coupled electrooculogram and calibrated by the button-press task, and 2) determine the relationship of unit discharge to horizontal acceleration, either with or without the compensatory eye movements evoked by vestibular stimulation. Based on their responses during vestibular stimulation and/or eye movements, neurons in the vestibular nuclei (77% of our sample was in the medial nucleus) could be divided into four groups...

Acceleration↗