Temporal structure of the spike trains in the neuronal impulses of the visual and sensorimotor areas of the rabbit neocortex during conditioned reflex activity

Conjugated spikes were singled out from successions of discharges of neurones in the rabbit's visual and sensorimotor neocortical areas acting in correlation. Their temporal structure was studied at intersignal intervals in transswitching of defensive positive and inhibitory conditioned reflexes and also in pseudoconditioning. The obtained results testify that conjugated discharges appeared for the most part periodically (in the average in 85% of fragments of unit activity). At positive and inhibitory conditioned reflexes, the frequency of periodical conjugated discharges belonged in most cases to the theta-rhythm range. At pseudoconditioning, periodical conjugated discharges were in the main of frequencies of delta-range (up to 4 Hz). The obtained results testify about a great significance of cortical neurones interaction in theta-range frequency at conditioned activity.     

Conjugation of unit activity in the visual and sensomotor areas of the rabbit neocortex during a conditioned reflex to sound and light

Conjugation of unit activity in the visual and sensorimotor neocortical areas was studied by means of histograms of cross- and autocorrelation in rabbits with conditioned reflex to light (1st group) and sound (2nd group). Relative number of neurones pairs acting in correlation in the areas remote from each other, in intersignal intervals both before and after stimuli did not differ in the 1st and 2nd groups. At the same time delays in neuronal discharges in one area after the other were different. In the 1st group animals there was a predominance of the number of visual area neurones discharging after sensorimotor with a delay up to 125 ms, in comparison with the number of sensorimotor area neurones discharging after the visual one. In the 2nd group rabbits the number of visual area neurones with such a delay of discharges after sensorimotor was less and, on the contrary, a predominance of sensorimotor area neurones was observed discharging after the visual one. The obtained results allow to suggest that neurones of the visual and sensorimotor neocortex areas form a single functional system in cases when conditioned and unconditioned stimuli are addressed to these areas and when only one of the studied areas is the projection zone for the combined stimuli. Organization of the neurones activity in systems in these two cases is different.     

Neuronal impulse trains of the visual and sensorimotor areas of the rabbit neocortex in calm wakefulness and pseudoconditioning

The conjugation of unit activity in the neocortical visual and sensorimotor areas during calm wakefulness and in intersignal intervals, in two groups of rabbits at pseudoconditioning was studied. The first group was presented in a random order with flashes and electrocutaneous stimuli, the second one--with sounds and electrocutaneous stimuli. The number of neurones pairs working in correlation during calm wakefulness is significantly less (35%) than during pseudoconditioning (49 and 50% in the first and second rabbits groups, respectively). During calm wakefulness and in both groups during pseudoconditioning, the number of pairs with delays of discharges of the visual area neurones after the sensorimotor one, and of the sensorimotor after visual up to 120 ms was equal. Comparison of the data on delayed neuronal discharges during calm wakefulness and pseudoconditioning with those obtained earlier with conditioned reflexes testifies that forestalling of visual area neuronal discharges by sensorimotor discharges is characteristic only for the activity of cortical projections of conditioned and unconditioned stimuli.     

Types of correlative relations of the neuronal impulses of the visual and sensomotor areas of the neocortex in the rabbit

Neuronal activity of the visual and sensorimotor cortical areas was simultaneously recorded in intersignal intervals in rabbits with conditioned reflexes to light and sound. ES-1020 computer built cross-correlation (CCH) and autocorrelation (ACH) histograms of impulse activity of the se neurones. Analysis of CCH form, built with a bin of 2 ms gave no convincing proofs of the presence of synaptic connections between neurone of the visual and sensorimotor cortical areas and of influences from a common source with few switchings on interneurones. Analysis of CCH built with bins of 10 and 30 ms, allowed to single out primary and secondary peaks and troughs. Wide primary peaks with the base covering the beginning of the coordinates, were met in 51.9% of cases; wide peaks, greatly shifted relatively to the coordinates beginning,--in 40.9% and trough--in 7.2% of cases. Secondary peaks did not always reproduce the ACH form of impulses trains of recorded neurones. The CCH analysis allowed to suggest two basic mechanisms, eliciting the correlated discharges--action of common input and influence of the neurones of one area on the other through a number of interneurones. It was not always possible to separate these two cases by means of CCH. In a number of cases, a more complicated character of neurones interaction could be suggested.     

A comparison of the spike train activity of the cortical neurons and of the spatial synchronization of the EEG

In chronic experiments EEG coherence and conjugation of impulse activity were compared of neurones of the visual and sensorimotor areas of rabbits neocortex simultaneously recorded with the same electrodes. Connection was revealed between the presence and properties of conjugated neurones activity and EEG coherence at various frequencies. At correlated neurones activity a greater EEG coherence was observed on frequencies of 3-4,5 Hz than at the independent activity. At the highest level of the EEG coherence the neurones discharged with less delay of one after the other in pairs, and in their synchronization a common source participated more often than at the lowest level of the EEG coherence.     

Correlation of neuronal reactions of different regions of the neocortex of the rabbit to conditioned positive and inhibitory stimuli

The activity of neurones of the visual and sensorimotor areas of the neocortex was simultaneously recorded in rabbits under the action of conditioned, inhibitory stimuli (CS, IS) and at simultaneous presentation of CS and the unconditioned stimulus (US) after trans-switching of the positive and inhibitory conditioned reflexes. Mean time of conjugated reactions of simultaneously recorded pairs of neurons is similar under the action of CS, combined action of CS and US and under IS. During the IS action as compared with CS, the phasic activity of some neurones in different areas increased, and due to this the similarity of reactions also increased; in other pairs of neurones the reactions weakened and the responses similarity decreased. The frequency of the appearance of intervals of the conjugated excitation after CS corresponds to 4.3 Hz; under combined action of CS and US it increases up to 5.9 Hz, and after IS--it decreases to 3.6 Hz. The order of coming into conjugated action of different pairs of neurones changes depending on the signal significance of the stimuli.     

The characteristics of the neuronal reactions of the cat somatosensory cortex to a heteromodal complex conditioned signal]

On alert cats the change was studied of the activity of the neurones of the sensorimotor cortical area at instrumental reaction to a simultaneous heteromodal complex stimulus. It was shown that in the projection of distal limb areas a group could be singled out of neurones, which changed their activity in one direction depending on the character of presented signals. In these cells an increase of discharges frequency was observed in response to complex stimulus, consisting of light and sound signals. After the extinction of the motor reaction both to the complex stimulus and to its components neuronal reactions of lesser intensity was recorded, what determined the absence of the motor reaction. This group of neurones had receptive fields localized on distal limb areas, it was activated at fulfillment of the movement of catching the reinforcement and belonged to neurones of the pyramidal tract. The neurones with receptive fields on the whole limb surface or changing their activity at the animal pose change, had variable reactions to positive and differentiation stimuli.     

The dynamics of the activating and inhibitory types of cortical neuron synchronization during the realization of a defensive reflex and internal inhibition

In the visual and sensorimotor areas of the neocortex and in the hippocampus of alert nonimmobilized rabbits, in response to combinations of light flashes with electrocutaneous limb stimulation an increase was observed of synchronization in the activity of the near-by neurones by activation by inhibitory type (coincidence of the presence and absence of impulse activity). In response to flashes against the light background--conditioned inhibitor--in the visual cortex synchronization of neurones increased by inhibitory type, and in the sensorimotor cortex and hippocampus changes of synchronization appeared, similar to the action of pain reinforcement but considerably weaker. The increase of synchronization by the activation type took place mainly in the neurones pairs with unidirected increase of impulses frequency and by the inhibitory one--with its decrease. Along with this, in a considerable part of neurones pairs both changes of synchronization appeared at the impulses frequency changes of different direction.     

Adaptability of the receptive fields of neurons of the posterior temporal cortex and their sensitivity to parameters of photic stimulation in the cat

Study of receptive fields (RFs) of neurones in the postero-temporal cortex (field 21) of alert cat at three levels of visual adaptation: light photopic, light mesopic and practically dark or extremely low scotopic adaptations--revealed invariance of the most part of the studied RFs to the level of visual adaptation. Reorganization of RFs, connected with change of background luminosity were observed only in 12% of visually activated neurones. Significant reduction of responses to optic stimulation is shown at increase of the level of luminosity in 75% of neurones, revealing adaptive reorganizations. It is suggested that these reorganizations may take place in analogy with neurones of the field 17 on account of different involvement of intracortical inhibitory mechanisms (and, probably, not only in the postero-temporal cortex, but also in structures which precede it in visual hierarchy). Study of neurones sensitivity in the field 21 to parameters of optic stimulation revealed their considerable invariance to the length and orientation of the optic stimulus moving through the RF (60% of cases). Testing of RF by a rhombic optic stimulus did not change neuronal reactions, the form and dimensions of RF did not significantly change.     

Activity of callosal neurons of the visual cortex in the cat

Activity of 28 identified neurones of the visual cortex was recorded in cats immobilized by d-tubocurarine. Stimulation of the callosal body with a single stimulus or high-frequency train elicited a short-latency antidromic reaction of neurones in the visual cortex whose axons constitute the main part of the large cerebral commissure. Some commissural neurones responded to a single callosal stimulation by two action potentials the first one being antidromic, the second one being of long-latency postsynaptic origin. The second action potential was generated as a result of activation of axonal collaterals of the same neurone or the neighboring callosal neurones. More than a half of callosal neurones responded to a single stimulation of the lateral geniculate body by short-latency antidromic discharges and by long-latency postsynaptic reactions. These data indicate the existence of the systems of two-way neuronal connections, i.e. calloso-geniculate and geniculo-callosal ones.     

The subcortical neuronal correlates of human assessment actions]

In patients with parkinsonism to whom in accordance with medical-diagnostic indices electrodes were implanted into the nuclei of thalamus and striopallidal system, impulse activity of neurones was recorded in tests with presentation of visual and acoustic stimuli. It has been shown that neurones of these structures, reacting by a change of discharges frequency in carrying out the assessing actions by man constitute a special class of neurones, spatially separated from those, connected with the organization of motor acts. The typical feature of neuronal reactions is a high degree of their value dependence on the level of attention. Neurones of the above structures reacts also during preparation of the assessing actions and fixation of their results in the short-term memory.     

Correlation of the neuronal impulse activity of different areas of the neocortex in rabbits in the switching of positive and inhibitory conditioned reflexes

By cross-correlation method conjugation in impulse activity of pairs of simultaneously recorded units in the visual and sensorimotor areas of the neocortex (representations of the conditioned and unconditioned stimuli) was studied during the switching of defensive positive and inhibitory reflexes in rabbits. 30-second fragments of impulse activity were analyzed in intervals before and after three presentations of positive and inhibitory conditioned stimuli (CS). The activity of single pairs of units in the process of stimuli presentation was characterized by instability. Only in 29% of 51 units' pairs the presence or absence of correlation between their discharges was stable. Analysis of activity of 75 pairs of units showed differences in impulse activity in inhibitory and positive tonic reflexes. The number of pairs of correlated units in about 30 s after inhibitory CS decreased (27%) in comparison with the interval before its action (52%). In the inhibitory tonic conditioned reflex, temporal intervals of discharges of one unit correlated with discharges of the second unit undergo changes. The obtained results testify that such parameter as the number of pairs of units with correlated activity in intersignal time interval is very important for the realization of motor reaction to conditioned stimuli.     

Neuronal specialization of the motor cortex in normal rabbits and following destruction of the visual cortex

The activity of neurones of the anterolateral part of the motor cortex in food-acquisition behaviour was compared in two control rabbits and in three rabbits after the operation of bilateral ablation of the striatal cortex. In two of three operated rabbits the pattern of behavioural specialization lost considerably the specificity peculiar to the motor cortex (predominance of G-neurones activated in grasping of food), approaching (but not becoming identical) the pattern of specialization of the visual cortex neurones: the number of G-neurones decreased in a half, and the number of L-neurones (activated in connection with the acts of instrumental food-acquisition behaviour which animals were trained to in the experimental cage) was doubled. Changes of the activity were significantly less expressed in the third operated rabbit. The number of the neurones activated in food-acquisition behaviour in operated rabbits in comparison with the control ones was reduced in the upper layers of the cortex and increased in the lower layers. The resemblance is discussed of the basic processes of animals learning and behaviour recovery.     

Cross-correlation analysis of the background activity of visual cortex cells separated by different distances in the alert rabbit

Values of correlation coefficients (CC) and forms of cross-correlation functions of impulse activity were studied in neurones recorded with one microelectrode or simultaneously with two sticked together microelectrodes with tangential distance between tips of 70 and 140 mcm. Three main types of cross-correlation functions were singled out differing by peaks form and modes positions. The greatest variety of forms and the greatest percentage of significantly correlated discharges of cellular pairs were found among the neurones recorded with one electrode. Mean CC of cells recorded with one electrode was significantly greater than mean CC of the neurones recorded with two microelectrodes. Comparison of the character of intercellular correlation with amplitudes of recorded spikes showed that discharges of neurones with greater amplitude mainly forestalled discharges of cells with low amplitude.     

Relationship between level of vigilance and changes in the receptive fields of the cat visual cortex]

The activity of 118 neurones of the primary visual cortex (17th field) was studied in unanesthetized cats, immobilized with d-tubocurarine, in a state of calm wakefulness and in strained attention, alarm. The strained attention was elicited by an air-puff directed to the corner of the closed eye, not used for the photic stimulation. Considerable rearrangments of the receptive field of neurones (94%) were observed in the state of strained attention. In the majority of the studied cortical cells (75%) during 10-30 minutes the excitatory centres of their receptive fields became narrower while their inhibitory periphery widened; in the cells with the inhibitory centres of the receptive fields they were larger in 80% of the cases. It is shown that with dark, mesopic and scotopic adaptation the major characteristics of the changes in the receptive fields remain unaltered. It is assumed that these effects have a behavioural value for the organism, because the created rise in the level of alertness is accompanied by a sharpening of the receptive fields, i.e. by a greater ability to a fine analysis and recognition of visual images.     

Background activity of neurones of the amygdaloid complex and its changes in response to hippocampal stimulation

The background activity of neurones of the amygdaloid complex (AC) and changes induced in it by stimulation of the fimbria and adjacent regions of the hippocampus were recorded by means of microelectrodes. Background activity of 40% of the neurones of the AC consisted of an irregular spike discharge, while that of 10% was regular. The remaining neurones showed a tendency to group discharges. High-frequency hippocampal stimulation at 200 pulses/sec inhibited activity of 37% and facilitated activity of 23% of the neurones. Responses began 20–300 msec after the onset of stimulation. Low-frequency stimulation at 0.5–8 pulses/sec facilitated discharges in 42.6% of neurones. The results obtained are discussed in relation to the influence of the hippocampus on AC activity.Institute of Physiology, Siberian Branch of the Academy of Sciences of the USSR, Novosibirsk. Translated from Neirofiziologiya, Vol. 3, No. 5, pp. 500–504, September–October, 1971.     

The dependence of the neuronal reactions of the sensorimotor cortex to a simultaneous complex stimulus on the level of the differentiation of its components]

On alert animals the change was studied of the neuronal activity of the sensorimotor cortical area of cats brain in dependence on the level of differentiation of the components of simultaneous heteromodal complex stimulus. According to the character of this dependence and a number of other parameters two groups of neurones were singled out in the sensorimotor cortex. It was shown that parameters of reactions of all recorded neurones of the sensorimotor cortex to the positive conditioned signal were the first established after consolidation of the animal conditioned motor activity. In the course of elaboration following parameters changed: expressiveness, intensity, duration and value of latency. Reactions of neurones of both groups to the inhibitory stimuli were stabilized only after consolidation of the habit of differentiation. Responses of the first group neurones changed only by the pattern of discharge, while the responses of the second group neurones could change by expressiveness of response, its sign, duration and value of latency. Oscillations of the differentiation level after finishing of the elaboration of inhibitory conditioned reactions affected only the responses of the second group neurones to complex components.     

Two families of acyl-CoA thioesterases in Arabidopsis

We have identified two families of acyl-CoA thioesterase (ACHs) in Arabidopsis thaliana. One family, consisting of AtACH1 and AtACH2, appears to be peroxisomal, as they have type-1 peroxisomal targeting sequences. The other family, consisting of AtACH4 and AtACH5, resides in the endoplasmic reticulum, as shown by green fluorescent protein studies. AtACH2 has been overexpressed in Escherichia coli and shows high levels of acyl-CoA thioesterase activity against both 16:0-CoA and 18:1-CoA. AtACH5 has also been overexpressed in E. coli, and shows thioesterase activity as well. ACHs have been characterized in other many other organisms and in various subcellular locations, but their true physiological role is not yet understood. Indeed, atach5 gene knockout mutants have no observable phenotype.     

Effect of substance P on behavior in the rabbit and the activity of cortical neurons during training

Subcutaneous injection of substance P to rabbits in a dose of 250 mcg/kg elicited a transitory disappearance of motor reactions to painful reinforcing stimuli and a reduction of their probability to reinforced and inhibitory light flashes, as well as a protracted heart rate increase and decrease of respiration rate. One third of the neurones recorded decreased their background firing level and or excitatory components of the reactions to reinforcement and conditioned light flashes. The decrease was most distinctly seen in the sensorimotor cortex and less pronounced in the visual cortical area and hippocampus. The influence of the substance P on different types of cortical inhibition was not the same. Tonic inhibition of neuronal activity in response to reinforcement was enhanced. Bioelectrical parameters which reflect an enhancement of inhibitory hyperpolarization during elaboration of internal inhibition (i.e. inhibitory firing delays and corresponding background and evoked slow potentials oscillations) were not changed.     

Supplementary motor area of the monkey: activity of neurones during performance of a learned motor task.

1. Recordings were made of the natural dischages of neurones in the supplementary motor area (SMA) of conscious monkeys trained to perform a stereotyped motor task with either hand. 2. Eighty % of the total population of cells showed modulation of their activity during particular movements of either limb. Two thirds of this group had a similar pattern of modulation regardless of whether the contralateral or ipsilateral hand was used. 3. The number of cells whose activity was related to movements of distal joints was approximately equal to that whose discharges occurred with proximal movements. 4. Only 5% of cells tested sent their axons into the pyramidal tract, and only 15% of units investigated showed responses to passive manipulation of the limbs. The effective afferent input usually was of a rather complex kind. 5. The findings suggest that the discharges of a large number of neurones in SMA are changing during particular movements of either arm, and that only a small number of cells receive afferent sensory input. These results contrast with those obtained in the primary motor area and suggest a different role for SMA the control of movement.