Unit responses in the posterior suprasylvian gyrus of cats to different stimuli

Extracellular responses of 151 spontaneously active neurons in a small area of the cortex of the posterior suprasylvian gyrus to flashes, clicks, and electrodermal stimulation were studied in unanesthetized cats immobilized with D-tubocurarine. Altogether 63% of neurons responded to the stimuli, of which flashes were the most effective. The proportions of polybi-, and monosensory responding neurons were 60, 18, and 22% respectively. Responding neurons were found throughout the thickness of the cortex, but most frequently at depths of 1000–2000 µ from the brain surface. The latent periods varied not only for different cells (from 20 to 90 msec to all stimuli), but also for the same cell. Responses were unstable, prolonged (over 1 sec) and complex in their dynamic pattern (several phases of increase and decrease in frequency of spontaneous discharges or merely a prolonged increase or decrease in its frequency). In the character of their responses the neurons were divided into 4 groups: 1) poly- and bisensory with equivalent responses to all stimuli; 2) poly- and bi-sensory with nonequivalent responses; 3) monosensory, and 4) nonresponding. The results show that this area of the posterior suprasylvian gyrus is part of the associative cortex with projection predominantly of the visual receptor.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 4, No. 4, pp. 375–383, July–August, 1972.     

Inputs to the torus semicircularis in the electric fish Eigenmannia virescens

Summary The posterior lateral-line lobe, contrary to present belief, projects bilaterally to the torus semicircularis, although the contralateral projection is considerably more extensive. The torus also receives bilateral inputs from the medial octavo-lateralis nuclear complex, the reticular formation, a sublemniscal nucleus, and the nucleus prae-eminentialis. Unilateral inputs to the torus were found originating from the ipsilateral mesencephalic tectum and the contralateral lobus caudalis of the cerebellum. Extensive commissural systems between the right and left torus are also described for the first time.     

Responses of electrosensory neurons in the torus semicircularis of Eigenmannia to complex beat stimuli: testing hypotheses of temporal filtering

The weakly electric fish, Eigenmannia, changes its frequency of electric organ discharges (EODs) to increase the frequency difference between its EODs and those of a jamming neighbor. This jamming avoidance response is greatest for frequency differences (i.e., beat rates) of approximately 4 Hz and barely detectable at beat rates of 20 Hz. A neural correlate of this behavior is found in the torus semicircularis, where most neurons act as low-pass or band-pass filters over this range of beat rates.This study examines two mechanisms that could possibly underlie low-pass temporal filtering: 1) Inhibition by a high-pass interneuron. 2) Voltage and time-dependent conductances associated with ligand-gated channels. These mechanisms were tested by recording intracellularly while employing stimuli consisting of simultaneous low and high beat rates. A neuron's response to the low beat rate was not diminished by the addition of the higher frequency jamming signal (thereby superimposing a high rate of amplitude and phase modulation onto the lower rate), and the inhibitory interneuron hypothesis is, therefore, not supported. Also, the responses to the high beat rate were not facilitated during maintained depolarization in response to the low beat rate.In some cases, particularly band-pass neurons, accommodation processes appeared to contribute to the decline in the amplitude of psps at high beat rates.     

Fine structure of the torus semicircularis of some teleosts

Fine structure of the torus semicircularis of the loach, carp, common eel and rainbow trout was studied by light and elecron microscopy. The torus semicircularis of each species is divided into four layers. The subependymal first layer comprises numerous unmyelinated fibers and their terminals which contain cored vesicles. The second and the third layers are composed of small cell bodies and their dendrites respectively. These layers develop equally in the four species and contain the usual axodendritic synapses. On the other hand, the fourth layer varies in different species. The mediumsized cells in this layer, which are inferred to be of the same origin as the small cells from their configuration and size, show differences in lamination in each species. Compared with the usual axodendritic synapse of the small cells, the medium-sized cells have quite different synaptic patterns, which include inhibitory and electrical as well as the usual excitatory chemical synapses. From these findings, the medium-sized cells are surmized to receive sound of different degrees of intensity from that received by the small cells, which may have an effect on feeding behaviors of the species. In the deepest portion of the torus semicircularis of all species, there are large multipolar cells on which numerous axon terminals synapse in much the same way as they do on the medium-sized cells. These findings suggest that the synaptic patterns in the torus semicircularis may depend not on the receptive cells in each layer but on the various characteristics of the afferent fibers.     

Unit responses in the anterior zone of the suprasylvian gyrus to peripheral stimuli of different modalities

Unit responses in the anterior zone of the suprasylvian gyrus to visual, electrodermal, and acoustic stimulation were investigated in experiments on unanesthetized cats immobilized with tubocurarine. Electrical activity was recorded from 131 units, 121 of which were spontaneously active. In 65.5% of cells responses consisted of a short or long increase or a decrease in intensity of spike activity. Most cells (58.2%) were monosensory. Responses to visual stimulation were given by 72% of neurons, to electrodermal by 61.6%, and to acoustic by 9.3%. The corresponding latent periods were 20–40, 20–30, and 15–20 msec. Responses of the same neurons to different peripheral stimuli were uniform or they differed in their dynamics. Intracellular recording gave responses in the form of EPSPs (amplitude 4–5 mV, duration 60–80 msec) or, rarely, IPSPs (amplitude 2–3 mV, duration 160–200 msec). The functional organization of the associative cortex and mechanisms of analysis of incoming afferent information are discussed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 4, No. 4, pp. 368–374, July–August, 1972.     

Unit responses of the sensomotor cortex to paired electrical stimuli

Unit responses of the sensomotor cortex to paired electrical stimulation and visual cortex, applied either simultaneously or after various delays (from 0 to 200 msec) depend on the order of application of the stimuli and on the interval between them. If stimulation of the sensomotor cortex was used in a conditioning role the response continued unchanged when the intervals between stimuli were increased to 200 msec. If, however, stimulation of the sensomotor cortex had a testing role interaction was observed between the stimuli so that responses to both first and second stimuli were blocked; this was exhibited most clearly for intervals of 40–80 msec between stimuli. The blocking effect persisted on some neurons with delays of up to 200 msec between stimuli, while the response of others to both the first and the second stimulus was restored.Institute of Higher Nervous Activity and Neurophysiology, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 5, No. 6, pp. 628–635, November–December, 1973.     

The cytoarchitecture of the torus semicircularis in the teleost Barbus meridionalis

The torus semicircularis of Barbus meridionalis is composed of two nuclei, the nucleus centralis and nucleus lateralis. Its cytoarchitecture was studied in sections stained by Nissl and Golgi-Colonnier techniques. In the nucleus lateralis two portions were identified: the ‘pars lateralis’ and the ‘pars medialis.’ Cytoarchitecturally, both portions are identical. They exhibit a layered structure in which there is an alternation of cell-poor and cell-rich laminae designated as: (1) the subependymal layer; (2) the layer of small cells; (3) the fibrillar layer; and (4) the layer of disperse cells. The subependymal layer consists of fine fibers and some small rounded-ovoid cells whose dendritic prolongations course horizontally or ventrally. The second layer has small, densely-packed cells with rounded-ovoid and triangular somata and a main dendritic trunk that courses ventrally. The third layer contains dendritic fields of the cells of layer two and of cells from layer four. The fourth layer is composed of fusiform neurons with two dendritic trunks of equal thickness, rounded-ovoid neurons with one or two main dendritic trunks and multipolar triangular stellate neurons with equal dendritic trunks. The nucleus centralis comprises a fibrillar cortex with a structure identical to that of the subependymal layer. There is also a cellular region with the same cell types as those found in the nucleus lateralis. These two nuclei thus compose the torus semicircularis of the barbel. They exhibit the same cytological characteristics and both are differentiated by their cytoarchitectural and functional orders.     

Unit responses of the second auditory area to acoustic stimulation

Responses of 116 neurons of the second auditory area to clicks were recorded extracellularly in experiments on unanesthetized cats immobilized with D-tubocurarine. Neurons with and without (54.6%) took part in the response to clicks. The unit response to a click consisted of 1 or 2 spikes or a short volley. Different neurons responded to clicks at different times. The latent period of 25.8% of all neurons recorded was 6.5–13 msec, of 70% it was 14–25 msec, and of 4.2% it was over 25 msec. Long-latency responses to clicks (40, 50, and 100 msec) also were recorded. The responding neurons were found throughout the thickness of the cortex, but more frequently in layers III and IV. No relationship was found between the depth of the neuron and its latest period. Responses consisting of EPSP, EPSP-spike, EPSP-spike-IPSP, EPSP-IPSP, and primary IPSP were recorded intracellularly from the neurons of this area. It was concluded from the results that neurons of the second auditory area can be activated by the arrival of an afferent volley along the geniculo-cortical pathway and also by the arrival of impulses from the first auditory area.     

Unit responses of the squirrel visual cortex to shaped visual stimuli

Visual cortical unit responses of the squirrelSciurus vulgaris to shaped visual stimuli (stationary and moving spots and bands) were studied. Neurons responding selectively to the direction of stimulus movement and orientation of lines and those not responding selectively to these features were distinguished. Many neurons, whether responding selectively or not to movement direction, were specifically sensitive to high speeds of movement, of the order of hundreds of degrees per second. This selectivity in neurons responding selectively to movement direction persisted at these high speeds, despite the short time taken by the stimulus to move across the receptive field. Neurons responding selectively to line orientation were sensitive to lower speeds of stimulus movement — from units to tens of degrees per second. Neuronal sensitivity to high speeds of stimulus movement is achieved through rapid summation of excitation from large areas of the receptive field crossed by the fast-moving stimulus. Selectivity of the response to movement direction is produced under these conditions with the aid of directed short-latency inhibition, inhibiting unit activity for stimulus movement in "zero" direction.     

Limits of phase and amplitude sensitivity in the torus semicircularis ofEigenmannia

Eigenmannia can detect modulations in the time disparity of signals received by different regions of the body surface as small as several hundred nanoseconds. This study presents recordings of single units in the torus semicircularis that are sensitive to time disparities (differential-phase) between a sinusoidal signal received by the head region and a similar signal received by the body surface caudal to the fish's pectoral fins. The sensitivity of units to differential phase, measured by the change in spike rate per unit change in time disparity, was greatest when small phase modulations, rather than stationary phase differences, were presented. Thresholds of differential-phase coders ranged from 6.5 microseconds to several hundred microseconds, with approximately 20% of the units having thresholds in the 5-10 microseconds range. For most cells, sensitivity to small modulations of differential-phase was relatively unaffected by time disparity 'offsets' within a range of several hundred microseconds. A threshold of 5-10 microseconds is still an order of magnitude higher than that measured in the Jamming Avoidance Response (JAR). Neurons that were sensitive to amplitude modulations (AMs) had thresholds as low as 0.05%. This value is comparable to that observed at the behavioral level.     

A quantitative analysis of ipsilateral tectal unit responses to moving stimuli in frogs

Ipsilateral retino-tecto-tectal (IRTT) units were recorded extracellularly in the rostral optic tectum of the frog (Rana esculenta). The activity of 79 superficial units (II type) was quantified in response to black disks of various sizes, moved vertically at various angular velocities and against a white background. The contrast ¦C¦ was constant during the experiments. Neuronal activity was analysed by two methods, yielding identical results:

Characteristics of unit responses of the cat cerebellar cortex to acoustic stimuli

Investigation of unit responses of the cerebellar cortex (lobules VI–VII of the vermis) to acoustic stimulation showed that the great majority of neurons responded by a discharge of one spike or a group of spikes with a latent period of 10–40 msec and with a low fluctuation value. Neurons identified as Purkinje cells responded to sound either by inhibition of spontaneous activity or by a "climbing fiber response" with a latent period of 40–60 msec and with a high fluctuation value. In 4 of 80 neurons a prolonged (lasting about 1 sec or more), variable response with a latent period of 225–580 msec was observed. The minimal thresholds of unit responses to acoustic stimuli were distributed within the range from –7 to 77 dB, with a mode from 20 to 50 dB. All the characteristics of the cerebellar unit responses studied were independent of the intensity, duration, and frequency of the sound, like neurons of short-latency type in the inferior colliculi. In certain properties — firing pattern, latent period, and threshold of response — the cerebellar neurons resemble neurons of higher levels of the auditory system: the medial geniculate body and auditory cortex.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 5, No. 1, pp. 3–12, January–February, 1973.     

Auditory responses in the torus semicircularis of the cane toad, Bufo marinus. I. Field potential studies

Field potentials have been recorded in the torus semicircularis of the toad, Bufo marinus, in response to brief tones presented in the free field. The amplitude of the potentials varied with the frequency of the stimulus and location of the electrode along the rostro-caudal axis of the torus. All frequencies in the auditory range evoked largest potentials when the stimulus was located in the contralateral auditory field. Potentials evoked by low to mid frequencies were largest when the stimulus was located near the line orthogonal to the long axis of the animal. For progressively higher frequencies, the optimal stimulus position was progressively more anterior in the contralateral field. In animals in which one eighth nerve had been sectioned, field potentials evoked by tones of low to mid frequency were less sensitive to changes in stimulus direction than in normal animals. However, the directional sensitivity of field potentials evoked by mid to high frequencies was similar in monaural and normal animals. These observations suggest that binaural neural integration is important in determining the directional sensitivity of field potentials in the torus evoked by low to mid frequencies but not for potentials evoked by mid to high frequencies.     

The cytoarchitecture of the torus semicircularis in the golden skink Mabuya multifasciata

The skink, Mabuya multifasciata, torus semicircularis was subdivided into the central (CN), the laminar (LN), and the superficial (SN) nuclei using Golgi and Nissl methods. The central nucleus consisted of small ovoid neurons surrounding a core of fewer large ovoid-triangular and fusiform neurons. The ovoid cells had scant cytoplasm and two to five dendritic trunks. Most of these processes were directed around the periphery of the central nucleus. The large neurons had clumped, darkly staining Nissl substance and a central nucleus. The sparse dendritic spine population on these cells increased distally on the three to five radiate dendrites. The laminar nucleus was present caudal and ventral to the central nucleus. At more rostral levels it was medial and dorsomedial to the central nucleus. The NL had three to five layers of ovoid and fusiform neurons. Scattered within these layers were a few ovoid-triangular neurons. Ovoid neurons had eccentric or central nuclei. The arborization of their dendrites was generally medial and lateral but was frequently oriented caudomedial and rostrolateral. Fusiform neurons had pale Nissl substance, central nuclei, and one to two dendritic processes. The ovoid-triangular neurons had dense, clumped Nissl substance and at least two dendritic trunks with few spines. The superficial nucleus was dorsal, lateral, and caudal to the central nucleus. Extending ventrolaterally around the central nucleus, the superficial nucleus became confluent with the laminar nucleus, ensheathing the central nucleus ventrally, laterally, and dorsally. Rostrally the central nucleus was covered by the layers of the laminar nucleus. Within the superficial nucleus were ovoid, fusiform and sparse ovoid-triangular neurons. The study indicated that the morphology of the torus semicircularis in the golden skink was similar to that in other lizards. This similarity correlates with the degree of development as it relates to the auditory function, but was independent of the type of inner ear restraint mechanism.