Responses of rabbit visual cortical neurons to intracortical electrical stimulation

Responses of rabbit visual cortical neurons to single and repetitive intracortical electrical stimulation were investigated. The stimulating electrode was located 0.7–1.2 mm away from the recording electrode. Response thresholds to single stimulation were as a rule 150–180 µA, whereas to series of stimuli they were 30–60 µA. The latent period to the first spike averaged 5–15 msec but the probability of the initial discharge was very low, namely 3–6%. With an increase in current intensity the duration of the initial inhibitory pause was increased in half of the neurons responding to it, whereas in the rest it was unchanged. After presentation of series of stimuli spontaneous activity was enhanced for a short time (4–6 sec). In about half of the cells the same kinds of discharge dynamics were observed in response to repetitive stimulation (frequency 0.25 Hz) as in responses to light, but more neurons with sensitization of discharge and fewer "habituating" neurons took part in responses to electrical stimulation. It is postulated that stimulation of a given point of the visual cortex evokes excitation of a local neuron hypercolumn and inhibition of neighboring cell columns.M. V. Lomonosov Moscow State University. Translated from Neirofiziologiya, Vol. 15, No. 4, pp. 412–419, July–August, 1983.     

Evolutionary specialization in mammalian cortical structure

Changes in neocortex size were a prominent feature of mammalian brain evolution, but the implications for cortical structure, and consequently for the functional significance of such changes in overall cortical size, are poorly understood. A basic question is whether functionally differentiated cortical areas evolved independently of one another (adaptive specialization) or were allometrically constrained to co-vary tightly with the size of the whole. Here, I provide comparative evidence for adaptive specialization of cortical structure. First, the sizes of individual areas differ significantly between taxa after controlling for overall cortical size. Second, an analysis of separate visual cortical areas reveals that these exhibit statistically correlated evolution, independent of variation in nonvisual areas. Third, visual cortex size exhibits correlated evolution with peripheral visual adaptations (eye morphology and optic nerve size) and with photic niche. Thus, the evolution of mammalian cortical structure was closely associated with specialization for different sensory niches.     

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.     

The stability of the behavioral specialization of the neurons

Constancy of connection between the activity of limbic cortex neurones and food-procuring behaviour was studied on rabbits during prolonged unit records. Comparison of activity in the first and the second halves of records was conducted according to the mean frequency during each stage of recording, the mean frequency in each of 10 selected acts of cyclic behaviour and also the probability of activation presence in these acts. It was shown, that behavioural specialization, determined by the criterion of presence of 100% cell activation in specific acts, did not change during recording. The volume of changes in the connection of neurone activity to behaviour in the process of record greatly depended on conditions of recording; at constant mean frequency of neurone activity during the whole time of recording the volume of these changes was minimal.     

Curiouser and curiouser: genetic disorders of cortical specialization

The processes by which cortical areas become specialized for high-level cognitive functions may be revealed by the study of familial developmental disorders such as dyslexia, dyscalculia, prosopagnosia, color agnosia and amusia. These disorders are characterised by the inability to integrate information across multiple areas and the consequent failure to develop representations of the knowledge of some category based on its associated attributes. In contrast, synesthesia may be seen as a hyper-associative condition, possibly due to a failure to properly segregate areas into distinct networks. Here, I consider recent advances in our understanding of the genetic and neurobiological bases of these conditions and the developmental mechanisms underlying the specialization of cortical areas and networks.     

Glucagon-like immunoreactivity in hypothalamic neurons of the rat

Summary Antisera specific for three different regions of pancreatic proglucagon were used to examine the distribution of such immunoreactivity in rat hypothalamus. Neurons in the supraoptic and paraventricular nuclei were immunoreactive with an antiserum against glucagon, but not with antisera directed towards the aminoterminal region of proglucagon (glicentin) or the glucagon-like peptide I sequence in the carboxyl-terminal region of proglucagon. These findings confirm a previous report of glucagon-like immunoreactivity in the supraoptic and paraventricular nuclei, but indicate that, while this material is immunochemically related to glucagon, it is not derived from a proglucagon-like precursor.     

Functional specialization of mouse higher visual cortical areas

The mouse is emerging as an important model for understanding how sensory neocortex extracts cues to guide behavior, yet little is known about how these cues are processed beyond primary cortical areas. Here, we used two-photon calcium imaging in awake mice to compare visual responses in primary visual cortex (V1) and in two downstream target areas, AL and PM. Neighboring V1 neurons had diverse stimulus preferences spanning five octaves in spatial and temporal frequency. By contrast, AL and PM neurons responded best to distinct ranges of stimulus parameters. Most strikingly, AL neurons preferred fast-moving stimuli while PM neurons preferred slow-moving stimuli. By contrast, neurons in V1, AL, and PM demonstrated similar selectivity for stimulus orientation but not for stimulus direction. Based on these findings, we predict that area AL helps guide behaviors involving fast-moving stimuli (e.g., optic flow), while area PM?helps guide behaviors involving slow-moving objects.     

Functional specialization of seven mouse visual cortical areas

To establish the mouse as a genetically tractable model for high-order visual processing, we characterized fine-scale retinotopic organization of visual cortex and determined functional specialization of layer 2/3 neuronal populations in seven retinotopically identified areas. Each area contains a distinct visuotopic representation and encodes a unique combination of spatiotemporal features. Areas LM, AL, RL, and AM prefer up to three times faster temporal frequencies and significantly lower spatial frequencies than V1, while V1 and PM prefer high spatial and low temporal frequencies. LI prefers both high spatial and temporal frequencies. All extrastriate areas except LI increase orientation selectivity compared to V1, and three areas are significantly more direction selective (AL, RL, and AM). Specific combinations of spatiotemporal representations further distinguish areas. These results reveal that mouse higher visual areas are functionally distinct, and separate groups of areas may be specialized for motion-related versus pattern-related computations, perhaps forming pathways analogous to dorsal and ventral streams in other species.     

Behavioral state-dependent thermal feedback influencing the hypothalamic thermostat

The experimental evidence on the behavioral state-dependent compartmentalization of temperature in the central nervous system of three homeothermic species has been reviewed to address the question of how selective brain cooling influences hypothalamic temperature regulation.     

Early cortical specialization for face-to-face communication in human infants

This study examined the brain bases of early human social cognitive abilities. Specifically, we investigated whether cortical regions implicated in adults' perception of facial communication signals are functionally active in early human development. Four-month-old infants watched two kinds of dynamic scenarios in which a face either established mutual gaze or averted its gaze, both of which were followed by an eyebrow raise with accompanying smile. Haemodynamic responses were measured by near-infrared spectroscopy, permitting spatial localization of brain activation (experiment 1), and gamma-band oscillatory brain activity was analysed from electroencephalography to provide temporal information about the underlying cortical processes (experiment 2). The results revealed that perceiving facial communication signals activates areas in the infant temporal and prefrontal cortex that correspond to the brain regions implicated in these processes in adults. In addition, mutual gaze itself, and the eyebrow raise with accompanying smile in the context of mutual gaze, produce similar cortical activations. This pattern of results suggests an early specialization of the cortical network involved in the perception of facial communication cues, which is essential for infants' interactions with, and learning from, others.     

Behavioral specialization in developing sciaenids and its relationship to morphology and habitat

Behavioral development of three species of marine sciaenid fish larvae was examined and related to their sensory morphology and habitat. Anti-predator behavior of the larvae was examined under different experimental conditions to isolate the roles of vision and mechanoreception. Spotted seatrout larvae maintained high levels of responsiveness even without visual cues but performed very poorly without mechanoreception. Loss of visual cues had no impact on the distance at which seatrout responded to the stimulus. Atlantic croaker generally performed best when vision was available. This species had low responsiveness without visual stimuli, and had smaller reactive distances when unable to use vision. Red drum were the most flexible in their use of sensory systems. For almost the entire larva period, responsiveness of red drum was equally high regardless of which sensory system was not available. In addition, reactive distances were unaffected when either visual or mechanoreceptive stimuli were eliminated. Thus, seatrout and croaker are sensory specialists, and red drum are sensory generalists. This is corroborated by previous studies on the sensory morphology of these species which showed that seatrout had more mechanosensory specialization, croaker had more visual specialization, and red drum were intermediate, with some enhancement of both systems. Behavioral data are interpreted in terms of habitat usage of the three species. Seatrout have the most restricted distribution over seagrass beds, croaker have a somewhat more flexible distribution, encompassing more open water habitats, and red drum have the most flexible range of habitats, using both vegetated and unvegetated portions of the estuary. These results indicate that even closely related species can exhibit different behaviors in order to better exploit the habitats in which they occur.     

Central thermosensitivity and the integrative responses of hypothalamic neurons

1. Hypothalamic thermosensitive neurons are important in the integrative regulation of body temperature. In addition to receiving afferent thermal input, their activity correlates with the stimulation of thermoregulatory mechanisms.

2. While cold sensitivity is synaptically mediated, warm sensitivity depends on inherent cellular responses. Warm sensitive neurons may also respond to other homeostatic variations, hormones, and endogenous mediators.

3. In contrast to peripheral thermoresponsiveness, which depends on conductance changes that regulate membrane potential, hypothalamic warm sensitivity relies on regulating the prepotential phase of the action potential.

4. Additionally, the recent morphologic characterization of these neurons supports the criterion for warm sensitivity.