Connection of the auditory cortex secondary zones with the auditory subcortical cerebral centers in the cat

As it has been demonstrated microscopically, the corticofugal fibers in the AII and Ep zones of the auditory cortex in all the auditory subcortical centers (medial geniculate body, posterior colliculi of the tectum mesencephali and the superior olive nuclei) terminate by means of single axodendritic synapses, having an asymmetrically active zone, and mixed (by their form) synaptic vesicles. Small and middle dendrites make their postsynaptic part. A comparison has been carried out on distribution and form of synapses, completing the projection fibers from the zone of the primary acoustic responses (AI) and of the primary acoustic zone (AIV). Basing on the morphological data, concerning distribution and form of the synaptic terminals, a suggestion is made that physiological influence of each acoustic cortex zone is different for the medial geniculate body and posterior colliculi of the tectum mesencephali, but it is unitypical for the superior olive level.     

Cortico-cortical connections between the auditory fields and the sensomotor area of the cortex]

In 18 cats by means of two methods--anterograde degeneration and retrograde transport of exogenic horseradish peroxidase--cortico-cortical connections of the auditory fields to the cortical sensomotor area have been studied. These connections have been stated to terminate in layers V-III of certain parts of the sensomotor area corresponding to the projections of the foreleg and the head. Initial neurons of the connections studied are pyramidal cells in layers III and II. They are situated in rostral and caudal parts of the fields AI and AII, but within these levels they occur in different areas of the auditory fields.     

Tonotopic organization of the ventrorostral zone of the auditory cortex region AII in cats

The tonotopic organization of the ventrorostral (VR) zone of cortical auditory area AII was investigated in acute experiments on cats anesthetized with nembutal and unanesthetized immobilized animals. Response with the lowest threshold arose in 92% of test neurons to presentation of one or several sound frequencies. The majority (54%) were "tuned" to one characteristic frequency (CF), 38% to several frequencies, and 8% had no clear-cut CF. A connection was found between location of a unit within the VR zone and its CF. Neurons with the highest CF were located in the ventrocaudal AII. An increase was noted in numbers of neurons with the lowest CF with increasing distance (rost-rally) from the VR location zone of neurons tuned to a high frequency. Going by response to acoustic stimuli of frequencies ranging between 1 and 24 kHz, length of the VR projection zone of the AII was found to measure 1.8–2.0 mm. Location of the test zone in relation to auditory cortex sulci varied substantially from one animal to the next.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 22, No. 2, pp. 178–184, March–April, 1990.     

Sensory projections to the cerebral cortex inPerodicticus potto edwarsi Bouvier

The cortical sensory projections of somatic, auditory, and visual origin have been mapped in the chloralosed potto. The pathways of the contralateral side of the body project in a classical somatotopic fashion to a large area SI, behind the motor cortex and the central sulcus. The latter constitutes the posterior boundary of the motor cortex only in its ventral part. In its middle zone the motor cortex extends to its posterior lip. Above the sulcus the motor zone is immediately adjacent to the preparietal area. Visual evoked potentials are recorded behind the transverse occipital sulcus with a maximal focus just caudal to an occipital dimple. The auditory area is situated between the sylvian and parallel sulci. No heterosensory potentials (visual or auditory) can be recorded from the somatomotor area, nor from any other part outside their primary projection area. An area of convergent somatic projection devoid of somatotopic organization is found between SI and the auditory zone and another one in front of the central sulcus. In view of the poor cortical heterosensory integration, the sensory projection system of the potto seems to be less developed than in the cat.     

Cochleotopic organization of the second auditory cortical area in the cat

The cochleotopic organization of the second auditory cortical area was investigated in cats anesthetized with pentobarbital by the evoked potentials method. Two independent representations of the cochlea were shown to exist in area AII: One in the dorsocaudal portion, the other in its ventrorostral portion. These projections of the cochlea differ in size and in the order of representation of its different parts. The dorsocaudal part of the auditory projection area of the cochlea, which extends over a distance of 2.6–2.8 mm from the center of the basal to the center of the apical focus, is arc-shaped. The order of arrangement of projections of different parts of the cochlea in this region of the auditory cortex coincides with that in the first auditory area, whereas the projection of the cochlea in the ventrorostral part of area AII, the length of which is 1.4–1.6 mm, has the opposite order of representation. The localization of projections of the cochlea in different cats shows considerable variability not only as regards anatomical topography of the auditory cortex, but also from one animal to another. The basal region of the cochlea was shown to project to a larger area of the cortex than the middle and apical portions taken together. It is suggested that the basal turn of the cochlea is functionally the most important for perception and primary analysis of auditory information.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 12, No. 1, pp. 18–27, January–February, 1980.     

Receptive fields of auditory cortical neurons in the cat

Receptive fields of auditory cortical neurons were studied by electrical stimulation of nerve fibers in different parts of the cochlea in cats anesthetized with pentobarbital. The dimensions of the receptive fields were shown to depend on the topographic arrangement of the neuron in the auditory cortex. The more caudad the neuron on the cortical projection of the cochlea in the primary auditory cortex, the more extensive its receptive field. The receptive fields were narrowest in the basal turn of the cochlea and were symmetrical with respect to their center. It is suggested that the region of finest discrimination of acoustic stimuli in cats is located in the basal region of the cochlea, i.e., in that part of its receptor system which has the narrowest receptive field and is represented by significantly more (than the middle and apical regions of the cochlea) nerve cells in the primary auditory cortex [1].A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 13, No. 5, pp. 467–473, September–October, 1981.     

Functional organization of auditory projections to somatosensory cortical areas in cats

The functional properties of fibers transmitting auditory impulses to somatosensory areas S_I and S_II were studied in anesthetized and waking animals by the evoked potentials method. The thresholds of evoked potentials in areas S_I and S_II are 15–35 dB higher than those of evoked potentials in the auditory projection areas. Tonotopical localization is absent in somatic areas. Experiments on anesthetized animals showed that the spread of impulses relating to acoustic stimuli of different frequencies into areas S_I and S_II is effected through area A_I and its connections with the above zones. Another pathway probably also participates in the conduction of impulses from clicks. Analysis of the time constants of the first positive potential suggested that the interneuronal organization of auditory projections to area A_I is less complex than that of projections to the somatosensory areas. Comparison of amplitudes of evoked potentials of different projection zones in area S_I showed that the projection of the head receives more auditory impulses than the projection zone of the forelimbs, confirming the morphological data published previously.     

Tonotopic organization of the dorsocaudal zone of cortical area aii in the cat

The tonotopic organization of the dorsocaudal (DC) auditory cortex area AII was investigated during acute experiments on cats anesthetized with Nembutal. A capacity for selective response to presentation of auditory stimuli at a certain frequency was found in 93% of the neurons investigated. It was further observed that 75% of these cells were characterized by their fine tuning to one characteristic frequency (CF), the remaining 26% had several CF, and 7% reacted with a spike response to acoustic stimulation at all test frequencies and had no clearcut CF. A relationship was found between the location of a unit within the DC zone and its CF level. Neurons with the lowest CF were located in the upper position of the sylvian gyrus near the posterior ectosylvian sulcus. The CF of neurons rose progressively in step with increasing distance between the site of microelectrode recording and the low frequency focus of the DC zone travelling along the sylvian gyrus in a ventrorostral direction. Distance between low and high frequency foci of the DC zone measured 2.5–3.5 mm. Location of this zone in relation to the auditory cortex sulci varied considerably from one animal to another. Neurons with similar CF levels and arranged on this basis in vertical cortical columns could vary substantially in the dimensions of their receptive fields, sharpness of tunining to their own CF, and firing response pattern.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 20, No. 2, pp. 220–227, March–April, 1988.     

Spatial perception of stimuli during unilateral exclusion of the temporal portion of the neocortex by cold]

Behavioral reaction of twelve cats were studied in conditions of inactivation by cold of the temporal area (AI, AII, Ep and partly I-T) of one hemisphere. A typical vestibular ataxy was observed: deflection of the cats when walking, circular movements in the direction of the inactivated temporal area. Orienting reactions both to acoustic and photic stimuli persisted, but their spatial localization was completely lost. In every case the animals exhibited a clear orienting reaction towards the inactivated hemisphere, regardless of the localization of the source of signal. Reactions ot pain and olfactory stimulations likewise proceded in one direction. such a one-sided perception of sounds in the case of inactivation by cold of the temporal neocortex of one hemispheres is apparently due to the functional elimination of contralateral auditory structures. Disturbance of adequate spatial perception of photic, pain and olfactory stimuli under similar conditions results from a sharp drop in the tone predominantly of the ipsilateral hemisphere.     

Adaptations in the Mouse Auditory System for Perception of Ultrasonic Communication Calls

Ultrasonic calls in the frequency range of 40–80 kHz play an important role in sound communication of house mice. The processing of ultrasounds is enhanced by overrepresentation of the corresponding frequency range in the inferior colliculus and auditory cortex. The latter has an ultrasonic field that is distinct from the tonotopy of the primary auditory cortex and has connections with brain areas of multi-sensory, motivational, and motor control. Mechanisms, such as critical band filtering and categorical perception, ensure that ultrasounds can easily be discriminated from other sounds of the mouse acoustic repertoire.     

Connections between the parietal cortex with the lateral suprasylvian gyrus (Clare-Bishop area) and auditory cortex in cats

Projections between areas 5 and 7 and the lateral suprasylvian gyrus (Clare-Bishop area) were investigated using anterograde degeneration techniques. This showed a topographic organization of projections from areas 5 and 7 to the lateral suprasylvian gyrus. Area 5 association fibers terminate mainly in the anterior portion of the lateral suprasylvian gyrus; this corresponds to the intermediate zone and anterior section of the posterior suprasylvian region. Area 7 efferents are located more caudally, terminating in the posterior section of the intermediate zone and in the posterior region, excluding the outer posterior limits. Fields 5 and 7 give rise to single efferent fibers terminating in the auditory cortex. Fibers from area 5 terminate in the medial ectosylvian and medial, sylvian gyri, i.e., in zones Al and AII or areas 22 and 50. A projection from area 7 terminates at the superior border of the medial ectosylvian gyrus, corresponding to the upper limit of zone A1 or areas 22 and 50.L. A. Orbeli Institute of Physiology, Academy of Sciences of the Armenian SSR, Erevan. Translated from Neirofiziologiya, Vol. 22, No. 6, pp. 739–745, November–December, 1990.     

Functional topography of afferent projections of the horizontal division of the nucleus of the diagonal band in the dorsolateral neocortex of the cat

EPs recording under Nembutal anaesthesia during stimulation of the medial section of the horizontal part of the diagonal band nucleus (HNDB) shows a wide spreading of HNDB afferentation over the neocortex: from the frontal area to the medial and some posterior parts of the auditory, parietal areas and Ep zone, with the least activation of the latter three regions and activation increasing intensity correspondingly in the somatic zones II, I (SII, SI), motor and frontal cortex. Such reduction of signals flow intensity oriented both in caudal and ventral directions of the cortex goes with foci of maximal activity of these signals in the motor, parietal areas and zones of representation of various body parts in SI and SII. Traits of similarity and differences of signal's projections in the neocortex from HNDB and thalamic relay nuclei have been revealed. A hypothesis is substantiated on different mechanisms underlying peculiarities of influences of these subcortical nuclei on the cortex depending on the type of their afferent-neuronal links in the latter and their functional role in the brain activity.     

Activity of 3-neuron cortical microsystems in the cat during conditioned reflex switchover

Multiunit activity in two projection cortical areas (visual and motor) was studied in cats at conditioned switch-over of defensive and alimentary responses to electrostimulation of the visual pathways. Interneuronal relations of three-neuronal cortical microsystems (intra-analyzer connections) and relations between microsystems in the visual and motor cortical areas (inter-analyzers connections) were analysed by the method of crosscorrelation of action potential trains. Similar interneuronal relations were revealed in the motor microsystems and different relations were found in visual ones at elaboration of conditioned switch-over. This apparently indicates the leading role of the cortical projection of the signal stimulus in integration of adaptive behavioural act. On the other hand, the presence of common bonds for alimentary and defensive situations as well as of specific ones for each of them was shown in the distribution of interneuronal connections between the analyzers. The former apparently provide for the realization of the conditioned effector movement of the animal occurring in both situations with participation of the same effector organ (the tongue) The latter determine the character of the specific adaptive reaction.     

Regeneration of the projection and synaptic connections of tympanic receptor fibers of Locusta migratoria (Orthoptera) after axotomy

The tergite nerve N6 of the first abdominal segment of the locust Locusta migratoria contains receptor fibers, from the tympanic organ, and hair sensilla as well as motoric axons. The nerve was axotomized in nymphal instars or adults, and the regeneration of nerve fibers was studied. The sensory fibers regrow and regenerate their projection pattern within the central nervous system. They recognize their specific neuropile areas even after entering the ganglion through different pathways. The receptor fibers of the tympanic organ reestablish synaptic connections to auditory interneurons, even though the physiological characteristics of the interneurons are not fully restored. This regenerative capability contrasts with the lack of regeneration of peripheral structures in locusts, but supports the described plasticity in the auditory system of monaural locusts (Lakes, Kalmring, and Engelhard, 1990). The motor fibers do not regenerate nerves innervating muscles of the body wall.     

Rapid activity-dependent sprouting of optic fibers into a local area denervated by application of beta-bungarotoxin in goldfish tectum

The retinotectal projection is known to be capable of extensive long-term expansion of connections, but it is not known how fast such changes can occur or what triggers sprouting of terminals. We studied sprouting of optic fibers into an area denervated by local microinjection of beta-bungarotoxin (β-BTX), a specific presynaptic neurotoxin with phospholipase A₂ activity that destroys nerve terminals at the neuromuscular junction. After injection of 0.1 pmol of β-BTX, the optic terminals fired spontaneously with decreasing amplitude and became silent within 1 to 2 h. Outside the injection zone, the retinotectal map was normal, so the silent zone was associated with a scotoma in the visual field. Horseradish peroxidase (HRP) staining of the entire optic nerve showed a denervated region at the injection site with beaded, degenerating fibers at its edge. Between 3 and 9 days later, optic units were recorded within the injection zone whose receptive fields lay just outside the scotoma in the visual field, indicating that intact surrounding terminals had sprouted into the area. These sprouts made functional connections, as indicated by field potential recordings and current source-density analysis. At this time, HRP staining also demonstrated retinal innervation within the injection zone. By 12 days, normal maps with no scotoma were recorded and HRP staining was normal at the injection site, indicating that the β-BTX-damaged fibers had regenerated to reclaim their tectal sites. The results show that the retinotectal projection of goldfish is very dynamic, since intact optic fibers can sprout into adjacent vacant postsynaptic territory within 2 to 3 days, much faster than previously reported. In a final experiment, we showed that this sprouting is activity-dependent, since it could be prevented by blocking retinal activity with intraocular tetrodotoxin (TTX) during the first 2 days postinjection, even though TTX block of activity does not block regeneration in this system. One possible mechanism for this rapidly triggered sprouting is that arachidonic acid liberated by β-BTX acts as a sprouting factor to attract surrounding healthy fibers into the denervated region but requires activity at the terminals to be effective. © 1996 John Wiley & Sons, Inc.     

Responses and properties of receptive fields of neurons in the visual projection zone of the pigeon hyperstriatum

Unit responses in the hyperstriatal region of the pigeon forebrain to the action of various visual stimuli were investigated. Particular attention was paid to the discovery of retinotopic projection in the Wulst region. It was shown that as the electrode was advanced in the caudal direction in the zone of visual projection of the hyperstriatum the receptive fields of the neurons recorded shifted in the opposite direction in the visual field. The receptive fields of neurons of the ventral and dorsal hyperstriatum lie higher in the visual field and are larger in diameter than those of neurons of the accessory hyperstriatum. Unit responses in the visual projection zone of the Wulst depend on the intensity of illumination, size, and speed and direction of movement of the test objects across the receptive field. The functional role of the retino-thalamo-telencephalic system in visual interpretation in birds is discussed and it is suggested that the Wulst region is comparable with the striatal and also with the frontal regions of the mammalian cortex.M. V. Lomonosov Moscow State University. Translated from Neirofiziologiya, Vol. 8, No. 3, pp. 230–236, May–June, 1976.     

Comparison of the Connectional Properties of the Two Forelimb Areas of the Rat Sensorimotor Cortex: Support for the Presence of a Premotor or Supplementary Motor Cortical Area

The existence of multiple motor cortical areas that differ in some of their properties is well known in primates, but is less clear in the rat. The present study addressed this question from the point of view of connectional properties by comparing the afferent and efferent projections of the caudal forelimb area (CFA), considered to be the equivalent of the forelimb area of the primary motor cortex (MI), and a second forelimb motor representation, the rostral forelimb area (RFA). As a result of various tracing experiments (including double labeling), it was observed that CFA and RFA had reciprocal corticocortical connections characterized by preferential, asymmetrical, laminar distribution, indicating that RFA may occupy a different hierarchical level than CFA, according to criteria previously discussed in the visual cortex of primates. Furthermore, it was found that RFA, but not CFA, exhibited dense reciprocal connections with the insular cortex. With respect to their efferent projection to the basal ganglia, it was observed that CFA projected very densely to the lateral portion of the ipsilateral caudate putamen, whereas the contralateral projection was sparse and more restricted. The ipsilateral projection originating from RFA was slightly less dense than that from CFA, but it covered a larger portion of the caudate putamen (in the medial direction); the contralateral projection from RFA to the caudate putamen was of the same density and extent as the ipsilateral projection. The reciprocal thalamocortical and corticothalamic connections of RFA and CFA differed from each other in the sense that CFA was mainly interconnected with the ventrolateral thalamic nucleus, while RFA was mainly connected with the ventromedial thalamic nucleus. Altogether, these connectional differences, compared with the pattern of organization of the motor cortical areas in primates, suggest that RFA in the rat may well be an equivalent of the premotor or supplementary motor area. In contrast to the corticocortical, corticostriatal, and thalamocortical connections, RFA and CFA showed similar efferent projections to the subthalamic nucleus, substantia nigra, red nucleus, tectum, pontine nuclei, inferior olive, and spinal cord.     

Interhemispheric connections of ocular-dominance columns in cats with binocular vision impairment

We have investigated the interhemispheric connections of areas 17 and 18 in cats with impaired binocular vision (monocular deprivation, uni- and bilateral strabismus). Monosynaptic neuronal connections were studied using microionophoretic injections of horseradish peroxidase in the single cortical columns and analsys of spatial distribution of retrogradely labelled callosal cells was performed. In the cases of monocular deprivation and strabismus, the spatial asymmetry and eye-specificity of interhemispheric connections are retained. Quantitative changes of connections are more pronounced in strabismic cats. In cats with binocular vision impairments, as well as in control ones, the width of callosal-recipient zone is larger than of the callosal cells zone. This may indicate that interhemispheric connections are non-reciprocal in the areas of cortex that are more distant from the projection of vertical meridian of visual field. We expect that there should be morpho-functional in the cells that are providing connections in opposite directions.     

Descending pathways connecting the male-specific visual system of flies to the neck and flight motor

Summary During sexual pursuit, male flies Sarcophaga bullata, stabilize the image of a pursued target on the dorso-frontal acute zone of their compound eyes. By retinotopic projection, this region is represented in the upper frontal part of the lobula where it is sampled by ensembles of male-specific motion- and flicker-sensitive interneurons. Intracellular recordings of descending neurons, followed by biocytin injection, demonstrate that male-specific neurons are dye-coupled to specific descending neurons and that the response characteristics of these descending neurons closely resemble those of male-specific lobula neurons. Such descending neurons are biocytin-coupled in the thoracic ganglia, revealing their connections with ipsilateral frontal nerve motor neurons supplying muscles that move the head and with contralateral basalar muscle motor neurons that control wing beat amplitude. Recordings from neck muscle motor neurons demonstrate that although they respond to movement of panoramic motion, they also selectively respond to movement of small targets presented to the male-specific acute zone. The present results are discussed with respect to anatomical and physiological studies of sex-specific interneurons and with respect to sex-specific visual behavior. The present study, and those of the two preceding papers, provide a revision of Land and Collett's hypothetical circuit underlying target localization and motor control in males pursuing females.     

Discrimination of signals simulating movement of a sound source by dogs after ablation of the auditory cortex

The ability to perceive a moving sound image at dichotic stimulation was studied by means of avoidance technique for decorticated (AI, AII, Ep) dogs. The bilateral ablation disturbed the temporal cue discrimination of the direction of movement. But the animals retained the ability to localize the moving signal using delta I-cue.