Focus Of Maximal Activity Research Articles

Spatial distribution of activity of the neurons of the visual cortex during stimulation with a flash of diffused light.

At different stages in the development of the response to a flash of diffused light, groupings of excited neurons in field 17 of the guinea pig continue to occur within the same cortical microzones. These zones are separated from neighboring microzones by narrow inhibition zones. The ensembles of cells participating in excitation form columns tapering with depth. The groupings of excited cells noted during a silent break indicates a grouping of inhibitory neurons. Three subgroups are distinguished within the ensembles according to the average dynamics of their impulse activity; the groups are reciprocally interrelated. One of the subgroups is in the lower layers of the cortex. This subgroup is characterized by stably localized foci of maximal activity; their dynamics, apparently reflecting groupings of corticofugal neurons, are sharply distinguished from the subgroups of the middle layers. The ensembles under investigation are considered to be one of the forms of activity of the structural-morphological units in the cortex.

Early positive component of the tectal evoked potential ofSqualus acanthias during electrical stimulation of the optical nerve

The evoked potential of the tectum opticum during electrical stimulation of the optic nerve was studied in acute experiments on the dogfishSqualus acanthias L. The negative phase of the "classical" negative-positive evoked potential of the contralateral hemisphere of the tectum opticum was shown to be a complex potential, including an early positive component. A similar potential also was recorded from the ipsilateral hemisphere. Enhancement of this positive potential on insertion of the recording electrode deep into the brain, its resistance to functional block on application of potassium chloride to the brain surface, and recording a similar potential from the surface of the floor of the third ventricle after extirpation of the tectum opticum are evidence of the nontectal location of the source of this evoked potential component. On the basis of existence of a focus of maximal activity in the rostral zones of the brain beneath the tectum opticum, and disappearance of the early positive component during functional block and extirpation of this brain region, it is concluded that a leading role in the generation of this component is played by thalamic nuclei.

Neocortical evoked responses and spike activity during startling in response to stimulation of the mesencephalic reticular formation.

1. Stimulation of the mesencephalic RF by a single pulse of current (of threshold strength for elicitation of the startle response) evoked a reticulocortical response (RCR) in the cortex (LP 2.5–3 msec) with a focus of maximal activity in the sensomotor cortex. The RCR recorded from the surface of the cortex is polyphasic and consists of early (a negative-positive complex) and late (negative and positive waves) components of the evoked response. RCRs from different regions of the cortex had a similar configuration but differed in the absolute and relative amplitude characteristics of the different phases. 2. Among the sensomotor cortical neurons with an initial response of excitation to stimulation of RF which were investigated (248 cells) two groups were distinguished. Neurons of the first group (136, LP 3–50 msec) showed correlation with the appearance of the various phases of the global surface potential: during development of the early and late negative phases of the RCR neurons in the upper level of the cortex (24.1 and 19.3% of neurons respectively) were involved in the response; the response of 25.5% of neurons in the lower layers correlated with the appearance of the early positive wave of the RCR. For neurons of the second group (112, LP > 50 msec) no correlation was found with waves of the cortical surface potential. Neurons with an initial inhibitory response (66 cells) changed their activity during recording of the early negative component of the RCR (lower level, 40.4% of neurons). During recording of the early positive potential, spike activity in neurons of the upper layers was slowed or ceased (19.7% of cells). 3. The results indicate that the flow of nonspecific impulses to the cortex along oligosynaptic pathways is destined mainly for cells in the upper level of the cortex. 4. It is postulated that the motor component of the unconditioned startle response arising to stimulation of RF may be triggered from subcortical structures.

Vestibular responses of neurons in the anterior suprasylvian gyrus in cats and their interaction with responses to acoustic and facial stimulation

Unit responses in the anterior sigmoid gyrus of cats anesthetized with chloralose (70 mg/kg) to vestibular nerve stimulation and their interaction with responses to acoustic and facial nerve stimulation were investigated. The focus of maximal activity of the vestibular projection was shown to lie a little rostrally to the anterior suprasylvian sulcus. The modality specificity of this part of the cortex to vestibular impulses is reflected in the shortest values of latent periods and the distinct phasic character of the responses, and also in the numerical preponderance of neurons with short-latency responses. Although considerable topographic overlapping of the vestibular projection by acoustic and somatosensory (facial zone) projections is found, the vestibular afferent input predominates over the other afferent inputs.

Electrophysiological investigation of hypothalamo-neocortical connections in Macaca mulatta.

Functional relations between phylogenetically different parts of the hypothalamus and the neocortex were studied by the method of recording evoked potentials (EP) and evoked single unit responses in acute experiments on monkeys (Macaca mulatta). The focus of maximal activity of EP and of single unit responses was found to be in the frontal association cortex, where evoked responses with the shortest latencies were recorded. During stimulation of the posterior hypothalamus, mainly unit responses of excitatory character were recorded in the neocortex, whereas during stimulation of the lateral hypothalamus mainly unit responses of inhibitory character were recorded.

Transcallosal modulation of a focus of maximal activity in the motor cortex.

Evoked potentials were recorded from 170 symmetrical points of the motor cortex in acute experiments on 10 cats anesthetized with chloralose and pentobarbital. Callosal influences on the focus of maximal activity (FMA) were studied during bilateral and unilateral electrical stimulation of the sciatic nerves at different strengths. During weak stimulation division of the corpus callosum was shown to broaden the FMA, but during strong stimulation the FMA was narrowed. It is suggested that transcallosal modulation in the intact brain leads to clearer demarcation of the FMA in the motor cortex and also increases the differences between FMAs arising during stimulation at different strengths.

Spatial configuration of rabbit superior collicular evoked response to punctiform afferent stimulation

Evoked potentials arising in the rabbit superior colliculus in response to punctiform stimulation of the receptive field were studied. This response has only negative polarity at the focus of maximal activity and does not exhibit reversal of the potential which is a characteristic feature of the response to diffuse stimulation. The evoked potential was recorded at depths of between 0.1 and 0.9–1.0 mm from the collicular surface, corresponding to the stratum griseum superficiale. The response disappeared when the stimulating spot was shifted through 4–6° away from the optical position. It is suggested that evoked potentials to punctiform stimulation can give more complete information on the location of different synapses.

Habituation in the somatosensory cortex

Responses of neurons without spontaneous activity ("silent") to prolonged stimulation of the mesenteric nerves were studied in cats anesthetized with chloralose (65–70 mg/kg) and immobilized with flaxedil. The results showed that neurons of the association and primary projection areas are characterized by habituation to prolonged stimulation of visceral nerves. The rate of development of habituation depends on the parameters of stimulation and on the cortical region studied. Habituation developed more rapidly in the association area and was slower to develop at the focus of maximal activity of the second somatosensory area. The special features of cortical habituation during visceral stimulation are discussed.

Cochleotopic organization of the primary auditory cortex in cats

The cochleotopic organization of the primary auditory cortex was studied by the evoked potentials method in cats anesthetized with pentobarbital. Two foci of maximal activity (dorsal and ventral) were found in the primary auditory cortex of 85% of animals during local electrical stimulation of different areas of the cochlea. Analysis of projection maps of the primary auditory cortex of the cats showed that different areas of the cochlea are presented in this region disproportionately. The basal portion projects to a larger cortical surface than the middle and apical portions together, evidence of inequality of representation of different parts of the receptor apparatus of the cochlea in the primary auditory area. Considerable differences were observed in the arrangement of projections of the cochlea in the primary auditory cortex of different animals.

Influence of the fascia dentata on sensory responses of hippocampal neurons in area CA3

1. Connections of FD with area CA3 are organized topically. In response to stimulation of FD a focus of maximal activity is found in area CA3 and it is displaced by 0.7–1.0 mm rostrally to the point of stimulation of FD, which corresponds to the oblique course of the mossy fibers. The focus of activity is bounded on both sides by zones with predominantly inhibitory responses of CA3 neurons to stimulation of FD; in more remote parts responses are absent. 2. Neurons of area CA3 lying in the zone of activity where they give gradually potentiated responses to stimulation of FD become areactive to sensory stimuli. Outside this zone normal reactivity to sensory stimuli is preserved. 3. During electrical stimulation of FD in conjunction with the action of sensory stimuli responses of area CA3 cells to electrical stimuli may be considerably changed (strengthened or depressed). 4. Suggestions are made regarding the role of impulses arriving from FD in the processes of extinction of sensory responses of neurons in hippocampal area CA3.

EEG patterns in children aged 6-7 years during formation of a complex motor-visual skill.

1. During the assembling of a mechanical toy from its parts by children aged 6–7 years, spatial synchronization of cortical potentials is strengthened. 2. When the skill is formed, the focus of maximal activity in children with a stereotyped form of activity is located in the inferior parietal regions; in children with variable activity it lies in the anterior zones of the brain. 3. During consolidation of the skill the number of interhemispheric correlations increases, evidence of an increase in the degree of paired activity in the work of the child's brain. 4. Differences in the topographic distribution of interhemispheric spatial synchronization of brain electrical activity depend on the character of problem solving activity. If the task is performed in a stereotyped manner, correlations are strongest in the left motor area and right inferior parietal region; in the case of variable performance, correlation is strongest in the left motor area and right frontal region.

Interaction between zones of the sensomotor cortex and hypothalamus during the formation of pain stress

Cross-correlation analysis of the tension rhythm in various zones of the sensomotor cortex relative to the posterior hypothalamus showed that during pain stress there is an increase in the phase shifts accompanied by a decrease in the cross-correlation coefficients. These changes varied within the sensomotor cortex. At the focus of maximal activity for pain projections (posteriorly to the bregma) they were less marked than outside it, especially in the more anterior zones of the cortex (anteriorly to the bregma).

Hypothalamic evoked potentials to vagus and sciatic nerve stimulation

Hypothalamic evoked potentials to stimulation of the cervical portion of the vagus nerve and the sciatic nerve were recorded in experiments on cats anesthetized with chloralose and immobilized with succinylcholine. When both monopolar and bipolar recording techniques were used the focus of maximal activity of both "visceral" and "somatic" evoked potentials was located in the supramammillary and posterolateral region of the hypothalamus. Responses in the tuberal and anterior hypothalamus occurred in most experiments after a longer latent period, their amplitude was lower, and they were less stable. Evoked potentials in the focus of maximal activity of the posterior hypothalamus are similar in all parameters to responses of the mesencephalic reticular formation. Evoked potentials to stimulation of the visceral nerve have a higher threshold of generation and a lower amplitude than the "somatic" responses and they are inhibited more strongly when the frequency of stimulation is increased. Evoked potentials arising in the hypothalamus in response to stimulation of the vagus and sciatic nerves are regarded as nonspecific responses of reticular type.

Disturbance and restoration of functions after division of spinal afferent pathways in the cat

The possibility and degree of recovery of motor and sensory functions in cats were studied after one-stage or two-stage bilateral division of the posterior columns and spinocervical tracts at the cervical level. Blocking the afferent inflow along these systems led to severe and prolonged disturbances of sensation and motor activity and was accompanied by a sharp decrease in nociceptive sensation. Weak (6–8 V) electrical stimulation of the skin of the limbs, which evoked a primary response of maximal amplitude in intact waking animals, evoked no electrical response in the somatosensory cortex of the chordotomized animals. However, on increasing the intensity of stimulation by 2, 3, or more times, low-amplitude negative waves with a spike latency of about 15 msec, together with slow late waves, were recorded in foci of maximal activity of the cortex. Recovery of motor activity and, to some extent, of proprioception was observed 2–4 months after injury; responses to tactile stimulation were not restored. In the course of compensatory reconstruction evoked activity in the somatosensory cortex did not recover. It is concluded that the recovery of motor activity in cats after injury to the afferent systems of the spinal cord can take place despite a considerable defect of somatic sensation.

Cortical projection zones of Pacinian corpuscles of the cat hind limb.

Primary responses of the group of Pacinian corpuscles located beneath the tendon of the second digit of the cat hind limb were recorded. The nerve trunk containing fibers running from the Pacinian corpuscles was stimulated electrically. The group of corpuscles was isolated from the rest of the body with connections through the nerve trunk intact and were stimulated mechanically. PRs were found in the contralateral hemisphere in the first somatosensory (SI), second somatosensory (SII) and motosensory (MSI) cortical zones. Four foci of maximal activity appeared in the projection areas: one in SII, a second in MSI, and two in SI. Details of the main parameters of the PRs for each zone are given.

Spatiotemporal characteristics of evoked potentials in the posterior ventrolateral nucleus of the cat thalamus

Evoked potentials (EPs) in the posterior ventrolateral nucleus (VPL) of the thalamus in response to electrical stimulation of the skin of the contralateral forelimb were studied. It was shown that they are formed by superposition of several electrical dipoles, one of which lies with two poles in VPL while the rest have one pole in VPL and the other in more caudal zones of the somatosensory system. The first phase of the EP in VPL consists of two components with different amplitude—frequency characteristics. The lability of the second component is low and it disappears if the frequency of stimulation rises above 20 Hz. The focus of maximal activity during contralateral stimulation of the skin of the forelimb occupies the same topographical position in VPL during development of the positive and negative phases of the EP. The steepness of rise of the ascending phase and the amplitude of the positive phase of the EP are greatest at the focus of maximal activity; in other regions the lines of equal steepness need not necessarily coincide with the equipotential lines; differences are especially noticeable in the sagittal plane.

Cortical projection of pulmonary receptors in the cat

1. In acute experiments on cats stimulation of the central end of the pulmonary branches of the vagus nerves by single electric pulses evokes primary responses in two areas of the cortex. The first lies on both sides of the rostral end of the coronal sulcus and the second in the region of the orbital gyrus. These areas coincide with the cortical projection area of the afferent fibers of the vagus nerve and must be regarded as part of this projection. 2. The electrographic characteristics of the evoked potentials in these areas show definite differences. In the first area electrical diphasic responses are most commonly recorded, the first phase being positive. In the evoked potentials of the second area the first positive phase is frequently reduplicated. In this zone an electrical response with an initial negativity is sometimes recorded. The latent period of the response in the region of the focus of maximal activity of the first zone is 13–18 msec, and of the second zone 10–20 msec. 3. A marked and rapid change in the volume of the lungs produces electrical responses in both areas with a latency of 60 to 800 msec. The shape of such evoked potentials resembles that of the primary responses produced by electrical stimulation of the pulmonary nerve.

Thalamic representation of the visceral afferent system communication I. Representation of the splanchnic nerve in the posteroventral thalamic nucleus of the cat

Experiments were performed on cats under nembutal-chloralose anesthesia treated with muscle relaxants. The animals were fixed in a stereotactic apparatus, and the central ends of the splanchnic, sciatic, lumbar, intercostal nerves and brachial plexus were excited by a single stimulus. Tactile stimuli were applied to the sacrolumbar, thoracic, and abdominal areas. Unipolar leads were used. The pickup electrode had a point 10–20 μ thick, and was introduced by a stereotactic instrument. The results of the experiment were controlled histologically. In each zone of representation of the splanchnic nerve there are three girdles which overlap. At the center of the zone there is a focus of maximal activity (FMA) where the primary response has a latency of 4.5–5.0 mseconds and an amplitude of the positive phase of up to 300 μv. Around the focus, the responses had a latency of 5–6 mseconds, and an amplitude 20–50 μv below that at the FMA. The secondary responses were recorded, and found to have a latency of 8–12 mseconds, and an amplitude 70–100 μv less than that at the FMA. The area of representation of the splanchnic nerve (FMA) was located in the n. ventralis posterolateralis between frontal planes 9 and 10 over the zero line, and occupied the median portion of the nucleus. It coincided with the area of representation of the body and trunk, and penetrated into the zones of the fore- and hindlimbs. Such overlap of the zones evidently represents the morphological and physiological basis for the widespread interaction of visceral and somatic function at the thalamic level.

Representation of the internal organs in the cerebral cortex and cerebellum of cats and dogs communication IV. Cortical representation of the pelvic and pudendal nerves in dogs

By recording primary responses, 2 zones of representation of the afferent fibers of the pelvic and pudendal nerves were found in the cortex of each cerebral hemisphere in dogs. The zones are bilateral, with their localization in fields I and II of the general somatic sensation, within the area of representation of the hind limb. The zones of representation of the pelvic and pudendal nerves overlap each other. However, each nerve has its own focus of maximal activity (FMA) which does not coincide with the FMA of another nerve.

Representation of the internal organs in the cat and the dog cerebral and cerebellar cortex

By recording primary responses in two cortical areas of the pudendal nerve, afferent fibers have been shown to run to the cortex of each cerebral hemisphere. The focus of maximal activity (FMA) of the first zone, i.e., the cortical area within which the primary responses occur at maximum amplitude and minimum latent period is usually located on the posterior cruciate gyrus. The FMA of the second zone is located on the anterior ectosylvian gyrus. Both zones lie in the area reptesenting the hindlimb. The cortical areas of the pudendal and pelvic nerves discovered previously by the present author overlap each other widely, though their FMA do not coincide. This signifies that for each of the nerves, within the boundaries of the common area in which primary responses occur, there is a small area in which maximum values are obtained.