Journal of Neurophysiology

Phillips, D. P.; Irvine, D. R.

doi: N/Apmid: 219155

Abstract 1. Extracellular microelectrode recordings have been made of 429 single neurons in the pulvinar-posterior (Pul-PO) complex and adjacent regions of the thalamus of cats anesthetized with either sodium pentobarbital or alpha-chloralose. Controlled acoustic stimuli were presented by sealed systems incorporating probe microphone assemblies. 2. Neurons in pulvinar, lateralis posterior, and nucleus posterior were unresponsive to acoustic stimulation. Few cells in medial PO were observed to receive acoustic input, while sensitivity to tonal stimuli was a general feature of driven cells in other PO divisions. 3. Cells in lateral PO were generally sharply tuned to stimulus frequency, while the majority of cells in magnocellular medial geniculate and intermediate division of PO were broadly tuned. 4. Neurons in lateral PO and magnocellular medial geniculate had short response latencies to acoustic stimulation. Cells in intermediate division of PO were more often long latency. 5. Divisions of PO could not be differentiated on the basis of their binaural properties. Cells receiving excitatory input from solely the contralateral ear (E/O) or fros with onset discharge patterns showed occlusive binaural interaction properties. For cells with multiple-component discharge patterns, individual response components frequently had different patterns of binaural input and/or interaction. 6. On the basis of their discharge patterns, short latency, and frequency-tuning properties, it is suggested that lateral PO and magnocellular medial geniculate might derive their acoustic input from different divisions of the inferior colliculus. In contrast, the long latencies of units in PO intermediate division suggests a corticofugal input. 7. These data support anatomical parcelations of the Pul-PO complex, and the suggestion that this complex might provide acoustic input to the association cortices is evaluated. Copyright © 1979 the American Physiological Society

Mower, G.; Gibson, A.; Glickstein, M.

doi: N/Apmid: 85698

Abstract 1. The superior colliculus projects to the dorsolateral nucleus of the pons. Retrograde transport of horseradish peroxidase (HRP) revealed that cells in the superior colliculus, which send their axons to the pons, lie in both superficial (III) and deep (IV--VII) layers. Superficial cells outnumbered deep cells. The inferior colliculus also projects heavily to the dorsolateral pontine nucleus. 2. Dorsolateral pontine visual cells were activated only by visual stimulation. Cells responsive to somatic or auditory stimulation were also found in the dorsolateral nucleus, and they too responded to only one sense modality. 3. Of the dorsolateral pontine visual cells, 69% were directionally selective. 4. Dorsolateral pontine visual cells were responsive to moving targets over a wide range of stimulus velocities. Velocities between 25 and 100 degrees/s were the most effective. No cells responded to a stationary stimulus. 5. Single-spot targets were the most effective stimuli. Stimulus size was a more important parameter than stimulus configuration. Many cells had inhibitory regions outside of their excitatory fields. 6. The excitatory receptive fields of dorsolateral pontine cells were very large (median, 1,100 deg2). 7. Nearly all receptive fields were centered in the contralateral visual hemifield, and 91% of the dorsolateral visual cells were activated from either eye. 8. We conclude that the visual cells in the dorsolateral nucleus have receptive-field properties that are similar to those of cells in the superior colliculus. The preference of dorsolateral cells for single-spot targets contrasts strongly with the multiple-spot preference of medial pontine cells, which receive their input from visual cortex. Copyright © 1979 the American Physiological Society

Irvine, D. R.; Huebner, H.

doi: N/Apmid: 430107

Abstract 1. Acoustic properties of single neurons in pericruciate, anterior lateral, and medial suprasylvian "association" areas were studied in chloralose-anesthetized cats using sealed stimulating systems incorporating probe microphone assemblies. 2. A total of 652 cells were isolated. Approximately 70% of the cells in each area were responsive to acoustic stimulation, and the majority of these cells were also driven by visual and/or somatosensory stimulation. 3. Association cortex neurons responded to tone- or noise-burst stimulation with an onset response of 16--50 ms latency. The onset response was found to be followed by a long period of suppression in those cases in which spontaneous activity was sufficiently high for this to be detected. 4. The majority of 56 units for which detailed frequency-tuning data were obtained had broad, irregular tuning curves extending over 5--6 octaves or more. A small proportion of association cortex cells exhibited sharp tuning comparable to that obtained in control recordings from cells in primary auditory cortex (AI). Although a number of broadly tuned units were rather insensitive, many cells--both broadly and sharply tuned--were of comparable sensitivity to AI cells. 5. Of the association cortex cells examined for binaural properties, 95% received excitatory input from each ear, and the dominant mode of binaural interaction in these cells was one of occlusion. The occurrence of occlusion at suprathreshold intensities reflected a tendency for monoaural and binaural intensity functions to asymptote at the same level. 6. The broad tuning, lability, and polysensory convergence exhibited by association cortex cells are similar to those of the so-called auditory lemniscal adjunct system. However, the binaural properties of association cells differ significantly from those of both the lemniscal line and adjuct components of the auditory pathway. 7. The homogeneity of acoustic and polysensory input to the three association fields is compatible with their input being derived from the single subcortical nonspecific projection system (reticular formation and medial/intralaminar thalamus) postulated by previous investigators. However, both neuroanatomical and neurophysiological evidence suggest that the lemniscal adjunct system and certain areas of periauditory cortex might also contribute to this input. Copyright © 1979 the American Physiological Society

English, A. W.

doi: N/Apmid: 430112

Abstract 1. Simultaneous electromyographic (EMG) records were obtained from a single-joint extensor muscle of each of the four limbs of intact cats during repeated overground stepping trials. 2. In each limb, the temporal spacing of step cycles was determined by measurements of the intervals between consecutive terminations of EMG activity, since this occurs in a consistent relationship to the removal of the limb from the ground. By measuring the latencies between step cycles so determined, the temporal spacing of step cycles between limbs was determined. Each latency was expressed as a function of step duration or as a phase interval. 3. Analysis of the cooordination of step cycles of both homologous limb pairs (the forelimbs and hindlimbs), both homolateral limb pairs (the fore- and hindlimb on the right and left sides), and both sets of diagonal limbs suggest that the step cycles of the four limbs are coordinated according to a few frequently occurring patterns. However, the representation of a large number of phase intervals between these preferred patterns indicates a substantial amount of variability in interlimb coupling. 4. Analysis of the interaction of different interlimb-coupling patterns indicates that during alternate coordination of hindlimbs, coupling of the other limbs is fairly predictable. The step cycles of the forelimbs and hindlimbs are spaced according to a trotting form of coupling. During in-phase coordination of hindlimbs, the patterns of coordination of the other limbs are more diffuse. Forelimbs step cycles are coupled via a number of different modes, as are those of the forelimbs and hindlimbs. 5. It is concluded that the step cycles of different limbs are coordinated, but the association of observed patterns of coordination with any known neural pathways or the interaction of neural pathways should be approached with caution. The variability about the frequently occurring patterns is interpreted as an expression of the faculatative capabilities of the neural mechanisms controlling locomotion. Thus, these data favor a model of interlimb control during stepping, which recognizes preferred patterns of coordination and the variability about these patterns. Copyright © 1979 the American Physiological Society

Antonini, A.; Berlucchi, G.; Marzi, C. A.; Sprague, J. M.

doi: N/Apmid: 430108

Abstract 1. Section of the posterior two-thirds of the corpus callosum eliminates almost completely the response of superior colliculus (SC) neurons to stimulation of the contralateral eye in split-chiasm cats. On the contrary, the responsiveness of SC neurons to stimulation of the contralateral eye is not abolished by a transection of the posterior and tectal commissures leaving the corpus callosum intact. The callosal section also reduces the number of SC receptive fields abutting the vertical meridian in the ipsilateral eye of split-chiasm cats. 2. In cats with intact optic pathways, a similar callosal section abolishes the SC representation of the ipsilateral visual field in the ipsilateral eye and also reduces the number of receptive fields adjoining the vertical meridian in the same eye. In the contralateral eye, the SC representation of the ipsilateral visual field is reduced in extension to about one-fifth of that seen in cats with intact commissures. 3. The results suggest that the corpus callosum is the main pathway for cross-midline communication of visual information at not only the cortical, but also the midbrain level. The corpus callosum may subserve this function because it contains uninterrupted crossed corticotectal projections or because it transmits visual information from one hemisphere to contralateral cortical areas projecting ipsilaterally to SC. The latter hypothesis is more likely but, in any case, the findings imply that the lack of interhemispheric transfer of visual learning in cats with a chiasmatic and callosal section may depend on a midline disconnection of both subcortical and cortical visual centers. 4. The corpus callosum is also responsible for the representation of the ipsilateral visual field of the ipsilateral eye in the cat SC. The SC representation of the ipsilateral visual field in the contralateral eye is due, in minimal part, to direct retinotectal connections from temporal retina and, for the largest part, to the corpus callosum. 5. Finally, the corpus callosum contributes to the representation of the contralateral visual field near the vertical meridian of the temporal retina in both split-chiasm and normal cats. This is probably due to the scarcity of direct retinotectal projections from this part of the retina and to their supplementation by corticotectal neurons influenced by the callosal afferents. Copyright © 1979 the American Physiological Society

McCreery, D. B.; Bloedel, J. R.; Hames, E. G.

doi: N/Apmid: 219156

Abstract 1. The purpose of these experiments was to compare effects of electrical stimuli applied in two regions of the brain stem that are the sites of origin of descending bulbospinal systems; namely, the nucleus gigantocellularis of Brodal (7) and the nucleus raphe magnus, on the responses of lumbosacral spinothalamic neurons to mechanical stimuli. 2. In cats anesthetized with alpha-chloralose, stimulating in either of these structures with single pulses of current while the spinothalamic neuron was tonically activated by a sustained mechanical pressure resulted in an increase in the excitability of the cell followed by a prolonged suppression of its impulse activity. 3. For different neurons, the latency of the excitation ranged from 4 to 18 ms following the brain stem stimulus, while the latency of the suppression ranged from 16 to 34 ms. 4. In general, the effects of stimulating in the reticular formation and in the raphe nuclei were similar. although quantitative differences were found in the effects of each on different spinothalamic neurons. On the basis of these two studies, it is argued that the reticulospinal and raphe-spinal systems exert qualitatively similar effects on the responses of spinothalamic neurons evaluated in this experiment. 5. A comparison of the magnitudes of the suppression phase evoked from several different sites in the ipsilateral reticular formation and nucleus raphe magnus suggests that the descending systems arising from both these structures may be quite heterogeneous. 6. Stimulation of both regions of the brain stem produced a much greater suppression of the response of the spinothalamic neurons to slowly changing or sustained mechanical stimuli than to transient stimuli. It is suggested that the effects of descending systems arising both in the raphe nuclei and in the reticular formation on the responses of spinothalamic neurons to a mechanical stimulus are at least as dependent on the time course of the mechanical stimulus as they are on its intensity. Copyright © 1979 the American Physiological Society

Vertes, R. P.

doi: N/Apmid: 219157

Abstract 1. The activity of 44 single brain stem gigantocellular neurons was recorded in the freely moving rat during the following four states: quiet waking (W), waking with movement (W-M), slow-wave sleep (SWS), and rapid eye movement (REM) sleep. 2. Cells were classified into three groups on the basis of the states in which they maintained their highest rate of discharge. The three cell categories were: movement-REM (MOV-REM), movement (MOV), and quiet waking (QW) neurons. The MOV-REM neurons, comprising 68% of the cell population, discharged significantly more during waking-movement and REM sleep than during either W or SWS. The MOV neurons, 16% of the cells, showed significant increases in activity only when the rat moved. The QW neurons, also 16% of the cells, typically maintained high rates of discharge in the absence of movement. 3. The MOV-REM neurons were further divided into two subclasses of cells--phasically and tonically discharging neurons. The phasic MOV-REM cells appeared to participate in phasic motor events of REM sleep and corresponding movements during waking. The pattern of activity of the tonic MOV-REM neurons suggested that they may be involved in the generation and maintenance of the theta rhythm of the hippocampus during waking-movement and REM sleep. 4. No cells were found to discharge significantly more in REM sleep or SWS sleep than in the other states, (i.e., no REM or SWS selective cells were seen). Copyright © 1979 the American Physiological Society

Bullier, J.; Norton, T. T.

doi: N/Apmid: 219159

Abstract 1. To examine the transmission of visual information through the lateral geniculate nucleus, we have studied the receptive-field properties of 65 X and Y optic tract axons and compared them with the receptive-field properties of X and Y LGN cells in paralyzed cats anesthetized with N2O/O2 (70/30%). The same experimental conditions and quantitative methods have been used as in the preceding study of LGN cells (2). 2. The spatiotemporal organization of the receptive fields of X and Y retinal axons are similar to those of X and Y LGN cells. X ganglion cell receptive fields show a simple center-surround organization, whereas Y ganglion cell receptive fields show a more complex organization with three concentric regions: a central region of center-type response, a region of mixed center-type and surround-type responses, and a region of surround-type response. 3. The inhibitory strengh of the surrounding region was tested with a centrally located flashing light spot of successively increased diameter. As in the LGN, the inhibitory strenght of the surrounding region was stronger in retinal X-cells than in retinal Y-cells, and the strength of the inhibition decreased as the diameter of the receptive-field center increased. 4. The decrease of the inhibitory strength of the surrounding region with increasing distance from the receptive-field center was similar in the retina and in the LGN for cells belonging to the same class (X or Y) and having the same receptive-field center size. 5. The differences in properties in the LGN between small-field X-, large-field X-, and Y-cells are best explained by assuming that they are driven, respectively, by small-field X, large-field X, and Y retinal ganglion cells. There does not appear to be a significant mixing of properties either between cells having different receptive-field center sizes. 6. The principal transformation we found between retinal and LGN units is that X LGN cells have sharply lower spontaneous activities and driven activities, as compared with X ganglion cells. Y LGN units show only a small decrease in spontaneous activity in comparison with Y ganglion cells. 7. We conclude that there is a significant alteration in the LGN only in the properties of X-cells, possibly by way of a strong inhibitory pool converging on X LGN units. We further suggest that this inhibitory pool plays a role in the modulation of transmission of information through the LGN only in the X channel, while the Y channel appears to be relatively unaffected. Copyright © 1979 the American Physiological Society

Gottlieb, G. L.; Agarwal, G. C.

doi: N/Apmid: 430116

Abstract 1. Sudden dorsiflexions and plantarflexions of the foot were imposed on normal human subjects under various states of voluntary activity. 2. Under conditions of constant muscle contraction, the myotatic reflex in soleus and lateral gastrocnemius muscles is linearly and highly correlated with the rate of muscle stretch. The slope of this curve characterizes part of the reflex arc "gain." 3. The gain is linearly proportional to the level of tonic voluntary activation. 4. The gain is reduced by tonic contraction of antagonists. 5. The above statements can be summarized by the following equation (formula: see text), where d theta/dt is the rate of joint rotation. Ts and Tat are measures of voluntary contraction (tension) of all the extensor and flexor muscles acting at the ankle. The term S represents the level of preexisting spinal excitability that can be altered by prior instruction to the subject. 6. A phasic voluntary contraction of the soleus muscle, which leads to muscle shortening, will alter the reflex gain. The gain initially increases with increasing rates of shortening, but at higher rates the gain is reduced. This is in contradiction to the observation for tonic activation as stated above and may be due to an inability of the coactivated fusimotor system to produce sufficiently rapid cocontraction of the spindle fibers. 7. During lengthening of a muscle caused by voluntary contraction of its antagonists, the myotatic reflex gain is reduced. 8. The above facts are interpreted to imply that a functional role for the myotatic reflex in the leg extensors is limited to conditions of postural maintenance or slow, precise movement. During rapid movement, the myotatic reflex is ineffective and load-compensating reactions are mediated by longer latency loops. 9. The duration of the myotatic reflex EMG is from 10 to 40 ms, too brief to be a simple response to a velocity-sensing receptor organ. Either the response is in large measure due to the initial burst of spindle activity that occurs at the start of a ramp stretch, or motoneuron pool dynamics act as a high-pass filter on afferent inputs. 10. In the anterior tibial muscle, the relationships between stretch velocity and reflex amplitude and tonic voluntary contraction and reflex gain are qualitatively similar to those found in the ankle extensors. Copyright © 1979 the American Physiological Society

Heldman, E.; Grossman, Y.; Jerussi, T. P.; Alkon, D. L.

doi: N/Apmid: 34673

Abstract 1. A number of observations, as listed below, suggested a cholinergic basis for inhibitory interactions between photoreceptors of the eye in the nudibranch mollusk Hermissenda crassicornis. 2. The isolated eyes synthesized and accumulated acetylcholine but not other putative neurotransmitter substances. Synthesis and accumulation were determined by electrophoretic separation of products that incorporated radioactive label. Electron microscopic visualization of clear round vesicles within the photoreceptors' somata and axon hillocks was consistent with synthesis and storage of acetylcholine within these cells. 3. Pharmacologic experiments indicated the presence of cholinergic receptors on the terminal branches of the photoreceptors, which are pre- and postsynaptic to each other. Carbachol or nicotine produced hyperpolarization of the photoreceptors' membrane accompanied by a reduction of the input resistance. The reversal potential of carbachol-induced hyperpolarization coincided with the reversal potentials of the IPSPs that followed, one for one, impulses of neighboring photoreceptors. Eserine often caused blockade of the IPSPs. This blockade was associated with substantial membrane hyperpolarization and reduction of membrane resistance. 4. Neuronal endings within the optic tract in the area of the photoreceptor's terminal branches stained for acetylcholinesterase. 5. The results of these different experiments, especially when considered together, strongly suggest, although by no means unequivocally demonstrate, that the neurotransmitter of the photoreceptors is acetylcholine. Copyright © 1979 the American Physiological Society