Investigation of detector properties of neurons in the visual system of the rabbit

Responses of neurons in the superior colliculi and visual cortex of rabbits to a black and white boundary moving in different directions were investigated. Neurons responding clearly to presentation of the black and white boundary moving in one direction (movement in the opposite direction led to inhibition of spontaneous activity) and neurons giving well-defined maximal responses to movement of this boundary in 2 or 3 directions were found in the superior colliculi. Neurons with a marked maximal response to the stimulus moving in 1 or 2 directions were found in the visual cortex. Nembutal has a powerful effect on the quantitative detector properties of visual cortical neurons and sometimes may completely inhibit unit activity.V. Kapsukas Vilnius State University. Translated from Neirofiziologiya, Vol. 4, No. 1, pp. 61–67, January–February, 1972.     

A new visual area on the inferior wall of the cat cruciate sulcus

Properties of 187 neurons in the inferior wall of the cruciate sulcus, in an area where electrical stimulation evoked unidirectional saccadic eye movements, were investigated in waking cats. Of the total number 172 responded to visual stimulation. Neurons in the surface layers of the cortex responded to simple visual stimuli: light or dark spots or bars, both stationary and moving at speeds of around 30 deg/sec. These neurons showed no selectivity as regards stimulus orientation but sometimes behaved selectively toward the direction of their movements. In the intermediate layers the maximal neuronal response was obtained to a model of a bird flaping its wings. Neuronal responses in the depth of the cortex were characterized by selectivity to movement of stimuli toward or away from the animal in a certain part of the visual field, irrespective of whether a light stimulus was presented against a dark background or a dark stimulus against the light background. Responses to visual stimulation were exhibited only if the animal was in a state of activation, when the EEG showed desynchronization, and they were absent in a state of quite wakefulness. No responses were obtained to auditory or somatic stimulation. Responses to visual stimulation were not found in neurons of the medial wall of the brain beneath the cruciate sulcus, but responses were recorded to eye movements of definite size or orientation. It is postulated that at least two contiguous retinotopically organized zones exist in this part of the brain. Activity of one of them is connected with visual function, that of the other with eye movements.Institute for Problems in Information Transmission, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 16, No. 6, pp. 766–773, November–December, 1984.     

Orientation-selective neurons in the squirrel visual cortex

The organization of receptive fields of neurons sensitive to orientation of visual stimuli was investigated in the squirrel visual cortex. Neurons with mutually inhibitory on- and off-areas of the receptive field, with partially and completely overlapping excitatory and inhibitory mechanisms, were distinguished. Neurons of the second group are most typical. They exhibit orientation selectivity within the excitatory area of the receptive field because, if the stimulus widens in the zero direction, perpendicular to the preferred direction, lateral inhibition is much stronger than if it widens in the preferred direction. Additional inhibitory areas (outside the excitatory area) potentiate this inhibition and increase selectivity. It is suggested that there is no strict separation of simple (with separate excitatory and inhibitory mechanisms in the receptive field) and complex (with overlapping of these mechanisms) neurons in the squirrel visual cortex.A. N. Severtsov Institute of Evolutionary Morphology and Ecology of Animals, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 11, No. 6, pp. 540–549, November–December, 1979.     

Responses of parietal associative neurons to stimulation of primary sensory areas

Responses of 251 neurons in the anterior part of the middle suprasylvian gyrus to stimulation of primary sensory (auditory, visual, somatosensory) areas and also to acoustic, visual, and somatosensory stimuli were studied in acute experiments on cats anesthetized with chloralose (40 mg/kg) and pentobarbital (20 mg/kg). Three groups of neurons were distinguished by their responses to stimulation of the primary sensory areas: those responding by an increased firing rate (117) or by inhibition (35) and those not responding (99). Responses of 193 neurons to stimulation of the peripheral afferent systems were analyzed. Neurons of the parietal associative cortex responded more frequently to cortical stimulation than to peripheral. By the duration of the latent period of their response to cortical stimulation the neurons were divided into three groups: those with short (less than 20 msec), medium (20–30 msec), and long latent periods (over 30 msec). The first group was the largest.Kemerovo State Medical Institute. Translated from Neirofiziologiya, Vol. 4, No. 5, pp. 524–530, September–October, 1972.     

Laminar distribution of neurons with different types of receptive fields in the rabbit visual cortex

Investigation of receptive fields of 232 primary visual cortical neurons in rabbits by the use of shaped visual stimuli showed that 21.1% are unselective for stimulus orientation, and 34.1% have simple, 16.4% complex, and 18.5% hypercomplex receptive fields, and 9.9% have other types. Neurons with different types of receptive fields also differed in spontaneous activity, selectivity for rate of stimulus movement, and acuteness of orientational selectivity. Neurons not selective to orientation were found more frequently in layer IV than in other layers, and very rarely in layer VI. Cells with simple receptive fields were numerous in all layers but predominated in layer VI. Neurons with complex receptive fields were rare in layer IV and more numerous in layers V and VI. Neurons with hypercomplex receptive fields were found frequently in layers II + III and IV, rarely in layers V and VI. Spontaneous unit activity in layer II + III was lowest on average, and highest in layer V. Acuteness or orientational selectivity of neurons with simple and complex receptive fields in layers II + III and V significantly exceeded the analogous parameter in layers IV and VI.A. N. Severtsov Institute of Evolutionary Morphology and Ecology of Animals, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 17, No. 1, pp. 19–27, January–February, 1985.     

Responses of medullary neurons to microstimulation of the "locomotor strip" in cats

Synaptic responses of medullary neurons to stimulation of the bulbar locomotor strip with a current of about 20 µA were studied by an extracellular recording method in mesencephalic cerebellectomized cats. The mean latent period of response of 177 neurons was 3.2 msec. Neurons in which synaptic responses appeared were located in both the lateral and the medial parts of the reticular formation, but short-latency responses were recorded predominantly in the lateral part. In response to a single stimulus 32% of neurons generated a discharge of 2–4 spikes. "Respiratory" neurons were not excited by stimulation of the locomotor point. The results indicate that neurons of the locomotor strip may have an excitatory action not only on each other, but also on neurons located medially. The possible mechanisms of the spread of activity to the superior cervical segments of the spinal cord are discussed.Institute for Problems in Information Transmission, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 13, No. 3, pp. 275–282, May–June, 1981.     

Unit responses of the thalamic and ventral anterior thalamic nuclei to electrical stimulation of thalamic relay nuclei in cats

Responses of 92 neurons of the reticular (R) and 105 neurons of the ventral anterior (VA) thalamic nuclei to stimulation of the ventrobasal complex (VB) and the lateral (GL) and medial (GM) geniculate bodies were investigated in cats immobilized with D-tobocurarine. Altogether 72.2% of R neurons and 76.2% of VA neurons responded to stimulation of VB whereas only 15.0% of R neurons and 27.1% of VA neurons responded to stimulation of GM and 10.2% of R neurons and 19.6% of VA neurons responded to stimulation of GL. The response of the R and VA neurons to stimulation of the relay nuclei as a rule was expressed as excitation. A primary inhibitory response was observed for only two R and three VA neurons. Two types of excitable neurons were distinguished: The first respond to afferent stimulation by a discharge consisting of 5–15 spikes with a frequency of 250–300/sec; the second respond by single action potentials. Neurons of the first type closely resemble inhibitory interneurons in the character of the response. Antidromic responses were recorded from 2.2% of R neurons and 7.8% of VA neurons during stimulation of the relay nuclei. Among the R and VA neurons there are some which respond to stimulation not only of one, but of two or even three relay nuclei. If stimulation of one relay nucleus is accompanied by a response of a R or VA neuron, preceding stimulation of another nucleus leads to inhibition of the response to the testing stimulus if the interval between conditioning and testing stimuli is less than 30–50 msec.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 8, No. 6, pp. 597–605, November–December, 1976.     

Unit activity of the posterior hypothalamus during brain and skin temperature changes in unanesthetized rabbits

Changes in the firing rate of posterior hypothalmic neurons in response to local elevation of the brain temperature by 0.6–1.5°C and to a rise and fall (separately and simultaneously) of the skin temperature by 3–5°C were investigated in unanesthetized rabbits. Neurons responding selectively to changes in brain temperature and skin temperature and neurons responding to both temperature stimuli were found in the posterior hypothalamus. During combined stimulation the unit activity was changed much more than in response stimulus. It is concluded that the region of the posterior hypothalamus participates in the integration of impulses from central and peripheral temperature receptors.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 5, No. 5, pp. 490–496, September–October, 1973.     

Organization of receptive fields of motion-senstitive neurons in the cat pulvinar

The distribution of 70 visually sensitive neurons in the cat pulvinar sensitive to motion in the receptive fields was studied. The experimental results showed that components with directional characteristics are present in the structure of these fields of both direction-selective and unselective neurons. In the receptive fields of direction-selective neurons the directional elements of the substructure have identical preferred directions, which coincide with the preferred directions of response to stimulus movement over the entire receptive field. The organization of receptive fields of direction-selective neurons of the visual association structure thus does not differ significantly from that of analogous fields of visual projection neurons. Directional elements of the receptive fields of direction-unselective neurons were found to have different preferred directions, thereby providing a basis for organization of the nondirectional response of the neuron to a stimulus moving across the entire receptive field.L. A. Orbeli Institute of Physiology, Academy of Sciences of the Armenian SSR, Erevan. Translated from Neirofiziologiya, Vol. 14, No. 4, pp. 339–346, July–August, 1982.     

Neurons with visual receptive fields independent of eye position in the caudal section of the ventral bank of cat cruciate slucus

Neurons responding to tactile and visual stimulation were found in the caudal section of the cruciate slucus ventral bank in awake cats. Tactile receptive fields were located on the face, mainly around the mouth. Visual stimuli evoked a response when presented close to the tactile receptive field. It was found that the visual responses of these bimodal neurons located in layer VI of the cortex display spatial consistency. The position of these visual receptive fields remained constant through saccadic eye movements, while still linked to the tactile receptive field.Institute for Research into Information Transmission, Academy of Sciences of the USSR, Moscow. Translated from Neifofiziologiya, Vol. 18, No. 6, pp. 800–805, November–December, 1986.     

Comparison of single unit responses in the vagal and facial lobes of the carp medulla to chemoreceptor stimulation

Responses of single neurons in the vagal lobe of the medulla to stimulation of chemoreceptors in the oral cavity and gills with solutions of hydrochloric acid and sodium chloride were studied in experiments on immobilized carp. These responses were compared with those of units in the facial lobe to stimulation of cutaneous chemoreceptors. The discharge frequency in the vagal lobe was lower and the latent period longer than in the facial lobe. In two parts of the primary chemoreception center different levels of analysis of gradations of the chemical stimulus were discovered. Neurons responding both to impulses arriving from both receptive zones and selectively to stimulation either of the mouth or of the gills, were found in the vagal lobe. Activity of volley type predominated in neurons of the vagal lobe during stimulation with sodium chloride solution.A. A. Zhdanov Leningrad State University. Translated from Neirofiziologiya, Vol. 10, No. 6, pp. 613–621, November–December, 1978.     

Electrophysiological investigation of medullary neurons connected with lateral line organs of the catfish (Ictalurus nebulosus)

Unit responses in the acoustic-lateral region of the medulla to electrical and mechanical stimulation of the lateral line organs were investigated in acute experiments on curarized catfish. Of the total number of neurons 70% possessed spontaneous activity. An electrical stimulus evoked a tonic response both in spontaneously active and in "silent" cells. Three main types of firing pattern of the neurons were distinguished: fast-adapting, slow-adapting, and grouped. As regards the relation of the neurons to polarity of the stimulus they were subdivided into two groups. The thresholds of unit responses to electrical stimulation varied considerably: from 2.5·10^–9 to 5·10^–12 A/mm². The effect of intensity of the electrical stimulation on unit responses in the medulla is analyzed. The precise dependence of on- and off-responses of each neuron on stimulus intensity of any polarity was determined. The neurons were shown to be sensitive to both electrical and mechanical stimuli. It is postulated that this phenomenon is due to convergence of impulses from electrical and mechanical receptors of the lateral line on the neurons. The properties of the central neurons are compared with those of the peripheral electroreceptor system in catfish.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 5, No. 2, pp. 156–163, March–April, 1973.     

Changes in reactivity of visual cortical neurons after local photic stimulation of their receptive fields in cats

Recovery cycles of unit responses in the primary visual cortex to local photic stimulation of their receptive fields were studied in unanesthetized, immobilized cats by the paired stimulus method. In most cases the process of recovery of neuronal reactivity did not follow a steady course. Recovery from depression evoked by the first stimulus took place more suddenly in neurons in the central part of the visual field, and initial recovery of activity was more complete than in peripheral neurons. Differences in the synchronization of inhibitory and excitatory inputs to neurons responsible for central and peripheral vision are discussed.Institute of Higher Nervous Activity and Neurophysiology, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 13, No. 3, pp. 233–240, May–June, 1981.     

Activity of propriospinal neurons during the scratch reflex in cats

Fictitious scratching, i.e., rhythmic activity of hind-limb motoneurons at the characteristic scratching frequency, was evoked by tactile stimulation of the ear in thalamic cats immobilized with flaxedil. Activity of propriospinal neurons in segments C₁, C₂, and T₄–T₇ was recorded extracellularly. The neurons were identified by their antidromic response to stimulation of their axons in segment L₁. Most neurons did not respond to stimulation of the ear. Some neurons, however, were activated during fictitious scratching. Neurons of the cervical segments responded not only to stimulation of the ear, but also to tactile stimulation of the forelimbs and also to passive movements of those limbs. Neurons of the thoracic segments were activated only by stimulation of the ipsilateral ear; these neurons were inhibited by stimulation of the contralateral ear. The role of the propriospinal neurons in the activation of the spinal mechanisms of scratching is discussed.Institute for Problems of Information Transmission, Academy of Sciences of the USSR, Moscow. M. V. Lomonosov Moscow State University. Translated from Neirofiziologiya, Vol. 9, No. 5, pp. 504–511, September–October, 1977.     

Functional characteristics of visual cortical neurons in squirrels

Depending on the organization of their receptive fields and character of their responses to shaped visual stimuli the following main groups of visual cortical neurons were distinguished in the squirrelSciurus vulgaris: nonselective for direction of movement and orientation of stimuli (14%); selective for direction of movement (30%) and selective for line orientation (49%); 7% of neurons were not classified. Cells selective for direction of movement and some nonselective cells exhibited specific sensitivity to high speeds of stimulus movement (optimal velocities of the order of hundreds of degrees per second). Neurons selective for line orientation differed in the degree of overlapping of their on- and off-zones; they could include analogs of simple and complex neurons.A. N. Severtsov Institute of Evolutionary Morphology and Ecology of Animals, Moscow. Translated from Neirofiziologiya, Vol. 13, No. 2, pp. 125–231, March–April, 1981.     

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.     

Neuronal response in the cat parietal association cortex to conditioned and non-conditioned acoustic stimuli

Neuronal response in the cat association cortex (area 5) to conditioned and non-conditioned acoustic stimulation was investigated. Numbers of neurons responding to a conditioned acoustic stimulus according to the traditional reflex pattern were twice as high. Numbers of inhibitory neuronal responses to the stimulus increased when instrumental reflex occurred. Neurons were found which only reacted to a conditioned acoustic stimulus in the absence of conditioned reflex movement occurring with instrumental food reflex. Although findings do not exclude the possibility of this cortical area contributing to the analysis of sensory signals and evaluation of their biological significance, it might be supposed that its main functional property lies in its involvement in the process of initiating behavioral response to a conditioned response.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 20, No. 5, pp. 637–645, September–October, 1988.     

Involvement of mesencephalic reticular formation neurons in cat conditioned reflexes

Traditional defensive and operant food reflexes were used to investigate neuronal responses of the mesencephalic reticular formation. It was found that these neurons may be divided into different groups according to function, depending on how they respond to positive conditioning stimuli. Of the two main groups of neurons with sustained tonic reactions one is activated in response to positive acoustic conditioning stimulation; it no longer reacts to the same stimulus after extinction of the reflex, while the other only becomes involved in response to positive stimulation accompanying the initiation of movement. Neurons belonging to the second group begin to respond directly to acoustic stimulation after extinction of the conditioned reflex. Neurons of the mesencephalic reticular formation can thus exercise additional tonic ascending effects both in the production and inner inhibition of the conditioned reflex. The group of neurons with a phasic reaction, i.e., a double response (a direct response to sound and another produced by movement) displayed a drop in spontaneous activity during the shaping of inhibition of differentiation and of extinction in particular. It was found that the initial changes in the spike response of reticular formation neurons during conditioning and pseudo-conditioning are similar. There are thus grounds for stating that neurons of the mesencephalic reticular formation participate in the shaping, production, and inner inhibition of traditional and operant conditioned reflexes in a differentiated capacity rather than as a population reacting identically.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 18, No. 2, pp. 161–171, March–April, 1986.     

Comparison of direct influences of the perforant path on hippocampal CA1 and CA3 neurons in vitro

The efficiency of synapses of the perforant path located on terminals of apical dendrites of CA₁ and CA₃ neurons was investigated in sections of the guinea pig hippocampus in vitro. Neurons of both areas were shown to respond to stimulation of the perforant path by action potential generation. Responses of most CA₁ neurons appeared to repetitive stimulation with a frequency of up to 30–80/sec. Neurons in area CA₃ respond only to low-frequency stimulation (under 5/sec). Posttetanic potentiation of responses to stimulation of the perforant path was found in both areas of the hippocampus.Institute of Biophysics, Academy of Sciences of the USSR, Pushchino-on-Oka. Translated from Neirofiziologiya, Vol. 11, No. 4, pp. 303–310, July–August, 1979.     

Convergence between influences from midbrain and bulbar locomotor sites and from an inhibitory site in neurons of the medulla

Synaptic response to regular stimulation of midbrain and bulbar locomotor sites (LS) and a pontine inhibitory site (IS) was recorded in medial and lateral bulbar neurons in cats (mesencephalic decerebellate preparation). Excitatory post-synaptic potentials (PSP) and discharges were usually noted in medial neurons; mixed PSP also occurred when stimulating the IS. Almost 50% of lateral and over 25% of medial neurons showed a change in background firing rate, failing to generate response time-locked to stimulus. Medial neurons producing a response time-locked to the stimulus showed equal sensitivity to stimulation of midbrain and bulbar LT and very little reaction to IS stimulation. Medial neurons with a response not time-locked to stimuli together with lateral neurons were most receptive to input from the bulbar LS, less sensitive to stimulation of the midbrain LS, and least responsive of all to IS stimulation. Convergence between influences from midbrain and bulbar LS was the same in neurons of all populations. The part played by different neuronal populations in initiation and cessation of locomotion is discussed.Institute for Research into Information Transmission, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 23, No. 3, pp. 297–306, May–June, 1991.