Prolonged excitation in the visual cortex of the cat

Intense light flashes produce maintained increased in cortical activity not dependent on continuous excitation from the retina.     

Unit responses to moving visual stimuli in the motor cortex of the cat

Neurons in the pericruciate cortex of the cat were tested with moving visual stimuli for responses to specific properties of the visual receptive field. Specific response patterns were shown by cells of origin of the pyramidal tract as well as by other cells.     

Interhemispheric synchronization of oscillatory neuronal responses in cat visual cortex

Neurons in area 17 of cat visual cortex display oscillatory responses that can synchronize across spatially separate columns in a stimulus-specific way. Response synchronization has now been shown to occur also between neurons in area 17 of the right and left cerebral hemispheres. This synchronization was abolished by section of the corpus callosum. Thus, the response synchronization is mediated by corticocortical connections. These data are compatible with the hypothesis that temporal synchrony of neuronal discharges serves to bind features within and between the visual hemifields.     

Universality in the evolution of orientation columns in the visual cortex

The brain's visual cortex processes information concerning form, pattern, and motion within functional maps that reflect the layout of neuronal circuits. We analyzed functional maps of orientation preference in the ferret, tree shrew, and galago--three species separated since the basal radiation of placental mammals more than 65 million years ago--and found a common organizing principle. A symmetry-based class of models for the self-organization of cortical networks predicts all essential features of the layout of these neuronal circuits, but only if suppressive long-range interactions dominate development. We show mathematically that orientation-selective long-range connectivity can mediate the required interactions. Our results suggest that self-organization has canalized the evolution of the neuronal circuitry underlying orientation preference maps into a single common design.     

Superior colliculus: single unit responses to stimulation of visual cortex in the cat

Electrical stimulation of area 18 of the cat visual cortex produces intense excitation of neurons in the superior colliculus. Excitation is followed by a period of decreased collicular responsiveness to light stimulation. These effects are seen in both directionally selective and nonselective units. The corticocollicular projection is retinotopically organized.     

Columnar architecture sculpted by GABA circuits in developing cat visual cortex

The mammalian visual cortex is organized into columns. Here, we examine cortical influences upon developing visual afferents in the cat by altering intrinsic gamma-aminobutyric acid (GABA)-mediated inhibition with benzodiazepines. Local enhancement by agonist (diazepam) infusion did not perturb visual responsiveness, but did widen column spacing. An inverse agonist (DMCM) produced the opposite effect. Thus, intracortical inhibitory circuits shape the geometry of incoming thalamic arbors, suggesting that cortical columnar architecture depends on neuronal activity.     

Neuronal correlates of eye movements in the visual cortex of the cat

About 10 percent of the cells in the visual cortex of awake cats do not respond to stationary parallel stripes in any orientation or to stripes moving across the visual field in any direction at a moderate speed (up to 132 degrees per second), but these cells are either excited or inhibited during saccadic eye movements when the animal faces a patterned visual environment. Of nineteen such cells tested in total darkness, seven discharged in association with eye movements. For saccade-related discharges, the latency during retinal stimulation is typically shorter than the latencey in total darkness.     

Contrast tuning in auditory cortex

The acoustic features useful for converting auditory information into perceived objects are poorly understood. Although auditory cortex neurons have been described as being narrowly tuned and preferentially responsive to narrowband signals, naturally occurring sounds are generally wideband with unique spectral energy profiles. Through the use of parametric wideband acoustic stimuli, we found that such neurons in awake marmoset monkeys respond vigorously to wideband sounds having complex spectral shapes, preferring stimuli of either high or low spectral contrast. Low contrast-preferring neurons cannot be studied thoroughly with narrowband stimuli and have not been previously described. These findings indicate that spectral contrast reflects an important stimulus decomposition in auditory cortex and may contribute to the recognition of acoustic objects.     

A micromechanical contribution to cochlear tuning and tonotopic organization

The response properties of hair cells and nerve fibers in the alligator lizard cochlea are frequency selective and tonotopically organized with longitudinal position in the organ. The lengths of the hair-cell hair bundles also vary monotonically with longitudinal position. In this study, quantitative measurements were made of the motion of individual hair bundles in an excised preparation of the cochlea stimulated at auditory frequencies. The angular displacement of hair bundles is frequency selective and tonotopically organized, demonstrating the existence of a micromechanical tuning mechanism.     

Comment on "Universality in the evolution of orientation columns in the visual cortex"

Kaschube et al. (Reports, 19 November 2010, p. 1113) argue that pinwheel density in three mammalian species follows a universal constant of π as predicted by their orientation-selective suppressive long-range connectivity model. We dispute their conclusions and suggest that a simple brain size-pinwheel density scaling law suffices in predicting the self-organized and disorganized orientation maps from primates to rodents.     

Two functional channels from primary visual cortex to dorsal visual cortical areas

Relationships between the M and P retino-geniculo-cortical visual pathways and "dorsal" visual areas were investigated by measuring the sources of local excitatory input to individual neurons in layer 4B of primary visual cortex. We found that contributions of the M and P pathways to layer 4B neurons are dependent on cell type. Spiny stellate neurons receive strong M input through layer 4Calpha and no significant P input through layer 4Cbeta. In contrast, pyramidal neurons in layer 4B receive strong input from both layers 4Calpha and 4Cbeta. These observations, along with evidence that direct input from layer 4B to area MT arises predominantly from spiny stellates, suggest that these different cell types constitute two functionally specialized subsystems.     

Voltage noise in Limulus visual cells

Intracellular recordings from Limulus eccentric cells suggest that the generator potential arises from the superposition of numerous discrete fluctuations in membrane conductance. If this is so, a relation between frequency response to flickering light and noise characteristics under steady light may be predicted. This prediction is verified experimentally. If a discrete fluctuation model is assumed, the data indicate that increased light has two major effects: (i) the discrete events are strongly light-adapted to smaller size, and (ii) the time course of each event becomes briefer.     

Number coding in association cortex of the cat

In electrophysiological investigations of single neurons in cortical association response areas of the cat, cells have been encountered that appear to code the property of number. In a sequence of stimulus presentations, these cells characteristically discharge to a particular numbered stimulus in the series. This effect is independent of stimulus modality, intensity, and interstimulus interval; thus, the cells seem to be responding to the number of stimulus presentations.     

The antidepressant fluoxetine restores plasticity in the adult visual cortex

We investigated whether fluoxetine, a widely prescribed medication for treatment of depression, restores neuronal plasticity in the adult visual system of the rat. We found that chronic administration of fluoxetine reinstates ocular dominance plasticity in adulthood and promotes the recovery of visual functions in adult amblyopic animals, as tested electrophysiologically and behaviorally. These effects were accompanied by reduced intracortical inhibition and increased expression of brain-derived neurotrophic factor in the visual cortex. Cortical administration of diazepam prevented the effects induced by fluoxetine, indicating that the reduction of intracortical inhibition promotes visual cortical plasticity in the adult. Our results suggest a potential clinical application for fluoxetine in amblyopia as well as new mechanisms for the therapeutic effects of antidepressants and for the pathophysiology of mood disorders.     

Human visual ecology and orientation anisotropies in acuity

The visual environment of Cree Indians from the east coast of James Bay, Quebec, is different from that of city-raised Euro-Canadians. So also are their corresponding orientation anisotropies in visual acuity. A Euro-Canadian sample exhibited the usual higher resolution for vertically and horizontally oriented gratings as compared with oblique orientations, while a Cree Indian sample did not. The most parsimonious explanation of these acuity differences is that orientation-specific detectors in humans are tuned by the early visual environment.     

Reward timing in the primary visual cortex

We discovered that when adult rats experience an association between visual stimuli and subsequent rewards, the responses of a substantial fraction of neurons in the primary visual cortex evolve from those that relate solely to the physical attributes of the stimuli to those that accurately predict the timing of reward. In addition to revealing a remarkable type of response plasticity in adult V1, these data demonstrate that reward-timing activity-a "higher" brain function-can occur very early in sensory-processing paths. These findings challenge the traditional interpretation of activity in the primary visual cortex.     

PirB restricts ocular-dominance plasticity in visual cortex

Experience can alter synaptic connectivity throughout life, but the degree of plasticity present at each age is regulated by mechanisms that remain largely unknown. Here, we demonstrate that Paired-immunoglobulin-like receptor B (PirB), a major histocompatibility complex class I (MHCI) receptor, is expressed in subsets of neurons throughout the brain. Neuronal PirB protein is associated with synapses and forms complexes with the phosphatases Shp-1 and Shp-2. Soluble PirB fusion protein binds to cortical neurons in an MHCI-dependent manner. In mutant mice lacking functional PirB, cortical ocular-dominance plasticity is more robust at all ages. Thus, an MHCI receptor is expressed in central nervous system neurons and functions to limit the extent of experience-dependent plasticity in the visual cortex throughout life. PirB is also expressed in many other regions of the central nervous system, suggesting that it may function broadly to stabilize neural circuits.     

Thermosensitivity of neurons in the sensorimotor cortex of the cat

Extracellular action potentials were recorded from 80 neurons in the sensorimotor cortex of the cat as brain temperature was varied by 4 degrees to 8 degrees C. The discharge rate of 37 percent of the neurons studied increased with increasing brain temperature. The discharge rate varied inversely with temperature in 11 percent of the neurons.     

Contextually evoked object-specific responses in human visual cortex

Human visual recognition processes are remarkably robust and can function effectively even under highly degraded viewing conditions. Contextual information may play a critical role in such circumstances. Here, we provide neurophysiological evidence that contextual cues can elicit object-specific neural responses, which have hitherto been believed to be based on intrinsic cues alone. Specifically, we find that the "fusiform face area" (FFA) maintains its selectivity for faces without regard to whether the faces are defined intrinsically or contextually. This finding further elucidates the role of the FFA and reveals neural correlates of contextual processing in the service of robust object recognition.