The role of visual experience in the development of columns in cat visual cortex

The role of experience in the development of the cerebral cortex has long been controversial. Patterned visual experience in the cat begins when the eyes open about a week after birth. Cortical maps for orientation and ocular dominance in the primary visual cortex of cats were found to be present by 2 weeks. Early pattern vision appeared unimportant because these cortical maps developed identically until nearly 3 weeks of age, whether or not the eyes were open. The na?ve maps were powerfully dominated by the contralateral eye, and experience was needed for responses to the other eye to become strong, a process unlikely to be strictly Hebbian. With continued visual deprivation, responses to both eyes deteriorated, with a time course parallel to the well-known critical period of cortical plasticity. The basic structure of cortical maps is therefore innate, but experience is essential for specific features of these maps, as well as for maintaining the responsiveness and selectivity of cortical neurons.     

Transient intra-areal axons in developing cat visual cortex

Transient axons reaching the medialmost part of area 17 were demonstrated with anterogradely transported biocytin injected in the dorsal part of the lateral gyrus in kittens during the first and second postnatal weeks. The axons decreased in number during the third postnatal week and were only exceptionally found thereafter. Computer-aided reconstructions from serial sections demonstrated axons with different degrees of complexity. The most complex ones were found at postnatal days 7-9 and were characterized by multiple branches terminating with growth cones in the white matter. Characteristically, endings of axons that entered the cortex remained confined to the infragranular layers V and VI. A few axons entered the supragranular layers. Transient axons terminated with different endings, which may indicate different stages of maturation. A few, possibly permanent, axons were still found in the medial part of area 17 at the end of the first, and during the second postnatal months; they arborized widely in the infragranular layers, and modestly or not at all supragranularly.     

Equivalence between temporal frequency and modulation depth for flicker response suppression: analysis of a three-process model of visual adaptation

We analyze adaptation processes responsible for eliciting and alleviating flicker response suppression, which is a class of phenomena characterized by the selective reduction of visual response to the ac component of a flickering light. Stimulus conditions were chosen that would allow characteristic features of flicker response suppression to be defined and manipulated systematically. Data are presented to show that reducing the sinusoidal modulation depth of an 11-Hz stimulus can correspond precisely to raising the temporal frequency of a fully modulated stimulus. In each case there is a nonmonotonic relation between flicker response and dc test illuminance. The nonmonotonic relation cannot be explained by adaptation models that postulate multiplicative and subtractive adaptation processes followed by a single static saturating nonlinearity, even when temporal frequency filters are incorporated into such models. A satisfactory explanation requires an additional contrast gain-control process. This process enhances flicker response at progressively lower temporal response contrasts as the illuminance of a surrounding field increases.     

Level-dependent representation of stimulus frequency in cat primary auditory cortex

The tonotopicity of the cat's primary auditory cortex (AI) is thought to provide the framework for frequency-specific processing in that field. This study was designed to assess this postulate by examining the spatial distribution of neurons within AI that are activated by a single tonal frequency delivered to the contralateral ear. Distributions obtained at each of several stimulus levels were then compared to assess the influence of stimulus amplitude on the spatial representation of a given stimulus frequency in AI. Data were obtained from 308 single units in AI of four adult, barbiturate-anesthetized cats, using extracellular recording methods. Stimuli were 40-ms tone pulses presented through calibrated, sealed stimulating systems. In each animal, the CF (stimulus frequency to which the unit is most sensitive), threshold at CF, response/level function at CF, and binaural interactions were determined for isolated neurons (usually one per track) in 60-90 electrode tracks. For each unit, regardless of its CF, responses to 40 repetitions of contralateral tones of a single frequency, presented at each of four or five sound pressure levels (SPLs) in the range from 10 to 80 dB were obtained. Different test frequencies were used in each of four cats (1.6, 8.0, 11.0, and 16.0 kHz). For tones of each SPL, we generated maps of the response rates across the cortical surface. These maps were then superimposed on the more traditional maps of threshold CF. All units whose CF was equal to the test frequency could be driven at some SPL, given an appropriate monaural or binaural configuration of the stimulus. There was a clear spatial segregation of neurons according to the shapes of their CF tone response/level functions. Patches of cortex, often occupying more than 2 mm2, seemed to contain only monotonic or only nonmonotonic units. In three cortices, a patch of nonmonotonic cells was bounded ventrally by a patch of monotonic cells, and in one of these cases, a second patch of monotonic cells was found dorsal to the nonmonotonic patch. Contralateral tones of any given SPL evoked excitatory responses in discontinuous cortical territories. At low SPLs (10, 20 dB), small foci of activity occurred along the isofrequency line representing the test frequency. Many of these cells had nonmonotonic response/level functions. (ABSTRACT TRUNCATED AT 400 WORDS)     

Developmental changes in infants' visual response to temporal frequency.

Investigated the development of visual responsiveness to variations in temporal frequency in 6 studies that were conducted when infants were at 4 and 6 mo of age. Groups of 12 infants each were tested in each study. In the 1st 2 studies, Ss viewed pairs of identical check patterns flashing at 2, 4, and 8 Hz, and their visual preferences were observed. When rate covaried with duty cycle (overall intensity), both age groups exhibited differential fixation as a function of frequency. To find out whether intensity variations were responsible for these results, intensity variations were eliminated (by equating duty cycle at 50%), and only frequency was varied. This manipulation resulted in the elimination of the previously observed differential response in the 4-mo-olds but had no effect on the 6-mo-olds' differential response. As a final check on the role of intensity, overall intensity was varied while temporal frequency was kept constant. Results show that 4-mo-old Ss continued to respond differentially whereas 6-mo-olds did not. These data show that at 4 mo of age Ss attended to the overall intensity of stimulation and ignored its temporal characteristics, whereas at 6 mo of age they no longer attended to the overall intensity and instead attended to temporal frequency per se. (14 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Associative connections of the visual area of the neuronally-isolated cat cortex

The associative pathways of the visual zone (fields 17 and 18) of the neuronal-isolated cortex of the cat were studied by the methods of Nauta-Gygax and Fink-Heimer. The cortex was isolated by the method proposed by M. M. Khananashvili (1961) by means of transection of projectional systems of the fibres connecting the cortex with subcortical structures in the site of their maximum concentration-in the internal capsule. Fields 17 and 18 were shown to have short associative pathways running both within the limits of the fields proper and to fields 17, 7 and to Clara-Bishop region disposed in the depth of the suprasylvian fissure. The site of termination of the associative libres was all layers of the cortex in some degree. It is assumed that the cytoarchitectonical fields in the neuronal-isolated cortex during conditioning interacts by means of intracortical fibres shown in the present investigation.     

Using response models to study coding strategies in monkey visual cortex

Usually the conditional probabilities needed to calculate transmitted information are estimated directly from empirically measured distributions. Here we show that an explicit model of the relation between response strength (here, spike count) and its variability allows accurate estimates of transmitted information. This method of estimating information is reliable for data sets with nine or more trials per stimulus. We assume that the model characterizes all response distributions, whether observed in a given experiment or not. All stimuli eliciting the same response are considered equivalent. This allows us to calculate the channel capacity, the maximum information that a neuron can transmit given the variability with which it sends signals. Channel capacity is uniquely defined, thus avoiding the difficulty of knowing whether the 'right' stimulus set has been chosen in a particular experiment. Channel capacity increases with increasing dynamic range and decreases as the variance of the signal (noise) increases. Neurons in V1 send more variable signals in a wide dynamic range of spike counts, while neurons in IT send less variable signals in a narrower dynamic range. Nonetheless, neurons in the two areas have similar channel capacities. This suggests that variance is being traded off against dynamic range in coding.     

Representation of spatial frequency and orientation in the visual cortex

Knowledge of the response of the primary visual cortex to the various spatial frequencies and orientations in the visual scene should help us understand the principles by which the brain recognizes patterns. Current information about the cortical layout of spatial frequency response is still incomplete because of difficulties in recording and interpreting adequate data. Here, we report results from a study of the cat primary visual cortex in which we employed a new image-analysis method that allows improved separation of signal from noise and that we used to examine the neurooptical response of the primary visual cortex to drifting sine gratings over a range of orientations and spatial frequencies. We found that (i) the optical responses to all orientations and spatial frequencies were well approximated by weighted sums of only two pairs of basis pictures, one pair for orientation and a different pair for spatial frequency; (ii) the weightings of the two pictures in each pair were approximately in quadrature (1/4 cycle apart); and (iii) our spatial frequency data revealed a cortical map that continuously assigns different optimal spatial frequency responses to different cortical locations over the entire spatial frequency range.     

Down-regulation of beta-adrenergic receptor following long-term monocular deprivation in cat visual cortex

To examine how adrenergic receptor binding is modified by experimental manipulation of sensory afferent, we carried out binding experiments (membrane fraction and in vitro autoradiography) for both alpha 2- and beta-adrenergic receptors in the brain of cats which had been deprived of vision in one eye. In the cerebral cortex of control animals, beta-adrenergic receptor (beta-AR) binding was found to be higher in the occipital regions than in other regions, while alpha 2-AR binding was relatively uniform. Monocular deprivation throughout the postnatal sensitive period (1-7 month of age) significantly decreased beta-AR binding in the visual cortex and lateral geniculate nucleus. Scatchard plot analysis in the visual cortex showed ca. 50% reduction in Bmax and little change in Kd. No significant difference was found in alpha 2-AR binding following monocular deprivation. Similar extent of down-regulation in beta-AR binding was confirmed in all layers of visual cortex using autoradiography.     

Functional topography of cat primary auditory cortex: response latencies

Minimum onset latency (Lmin) of single- and multiple-unit responses were mapped in the primary auditory cortex (AI) of barbiturate-anesthetized cats. Contralateral Lmin for multiple units was non-homogeneously distributed along the dorso-ventral/isofrequency axis of the AI. Responses with shorter latencies were more often located in the central, more sharply tuned region while longer latencies were more frequently encountered in the dorsal and ventral portions of the AI. For single units, a large scatter of Lmin values was found throughout the extent of the AI including cortical depth. The relationship between Lmin and previously reported spectral, intensity and temporal parameters was analyzed and revealed statistically significant correlations between minimum onset latency and the following response properties in some but not all studied animals: sharpness of tuning of a frequency response area 10 dB above threshold, broadband transient response, strongest response level, monotonicity of rate/level functions, dynamic range, and preferred frequency modulation sweep direction. This analysis suggests that Lmin is determined by several independent factors and that the prediction of Lmin based on relationships with other spectral and temporal response properties is inherently weak. The spatial distribution and the functional relationship between these response parameters may provide an important aspect of the time-based cortical representation of specific features in the animal's natural environment.     

Plasticity of neuronal response properties in adult cat striate cortex

We have utilized an associative conditioning paradigm to induce changes in the receptive field (RF) properties of neurons in the adult cat striate cortex. During conditioning, the presentation of particular visual stimuli were repeatedly paired with the iontophoretic application of either GABA or glutamate to control postsynaptic firing rates. Similar paradigms have been used in kitten visual cortex to alter RF properties (Fregnac et al., 1988, 1992; Greuel et al., 1988; Shulz & Fregnac, 1992). Roughly half of the cells that were subjected to conditioning with stimuli differing in orientation were found to have orientation tuning curves that were significantly altered. In general, the modification in orientation tuning was not accompanied by a shift in preferred orientation, but rather, responsiveness to stimuli at or near the positively reinforced orientation was increased relative to controls, and responsiveness to stimuli at or near the negatively reinforced orientation was decreased relative to controls. A similar proportion of cells that were subjected to conditioning with stimuli differing in spatial phase were found to have spatial-phase tuning curves that were significantly modified. Conditioning stimuli typically differed by 90 deg in spatial phase, but modifications in spatial-phase angle were generally 30-40 deg. An interesting phenomenon we encountered was that during conditioning, cells often developed a modulated response to counterphased grating stimuli presented at the null spatial phase. We present an example of a simple cell for which the shift in preferred spatial phase measured with counterphased grating stimuli was comparable to the shift in spatial phase computed from a one-dimensional Gabor fit of the space-time RF profile. One of ten cells tested had a significant change in direction selectivity following associative conditioning. The specific and predictable modifications of RF properties induced by our associative conditioning procedure demonstrate the ability of mature visual cortical neurons to alter their integrative properties. Our results lend further support to models of synaptic plasticity where temporal correlations between presynaptic and postsynaptic activity levels control the efficiency of transmission at existing synapses, and to the idea that the mature visual cortex is, in some sense, dynamically organized.     

The location of noisy visual stimuli.

Examined the results of experiments where Ss were required to detect the misalignment of 2 abutting dot clusters on a monitor screen. Thresholds varied with the square root of dot density and did not appear to be affected by changing the sampling strategy used to generate the random dot clusters. Comparison of the Ss' performance with that expected of 3 information processing strategies suggested that Ss accomplished the task by locating the edges of the dot clusters rather than by extracting measures of global scope or of central position. The efficiency with which edge information was extracted was approximately 50% for low-density stimuli and declined exponentially with increasing dot density. (French abstract) (18 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Influence of the presentation of remote visual stimuli on visual responses of cat area 17 and lateral suprasylvian area

Single units were recorded extracellularly from area 17 and lateral suprasylvian area (LSSA) in curarized cats. Visual stimuli, usually a 10 degree black spot, were introduced abruptly in the visual field remote from the discharge area of a neuron's receptive field and moved at a speed of about 30 degrees/sec. The effect of these remote stimuli (S2) on the reponse to a restricted visual stimulus (S1) crossing the discharge area was studied. It was found that most units in area 17 were not affected by the presentation of remote stimuli, the remainder being either slightly facilitated or slightly inhibited. In contrast the LSSA neurons were usually inhibited by the presentation of S2: this effect was strong, was present in all classes of LSSA neurons and was independent of the relative directions of movement of S1 and S2. On the basis of these data and those previously obtained from the superior colliculus it is concluded that the way the extrageniculate centres respond to a stimulus abruptly introduced in the visual field is substantially different from that of the striate cortex. Only in the extrageniculate centres a new stimulus, besides exciting the neurons which correspond to the position of the stimulus in the field, concomitantly decreases the responses of neurons located in positions of the visual field remote from that stimulus. Possible behavioral implications of the findings are discussed.     

The mismatch negativity to frequency deviant stimuli during natural sleep

Eight subjects spent a single night in the sleep laboratory. Event-related potentials (ERPs) were recorded during the presentation of two auditory "oddball' stimulus conditions in which tonal frequency was manipulated. In the first condition, 1000 Hz "standard' and 2000 Hz "deviant' tones were presented. In the second condition, the deviant tone was reduced to 1050 Hz. In both conditions, deviant probability was 0.2. Stimuli were presented every 600 ms during wakefulness and stages 2, 4, and REM of sleep. A distinctive N1 wave was visible in both stimulus conditions when the subject was awake. The deviant stimuli elicited a "mismatch negativity' (MMN) that inverted in polarity at the mastoid. In REM sleep, an N1 and a MMN were also elicited in both conditions. In the large deviance condition, the MMN had a slightly attenuated amplitude and was shorter in duration while in the small deviant condition, its peak latency was unusually early. Neither the N1 nor the MMN could be recorded in non-REM sleep.     

An intracellular study of the contrast-dependence of neuronal activity in cat visual cortex

Extracellular recordings indicate that mechanisms that control contrast gain of neuronal discharge are found in the retina, thalamus and cortex. In addition, the cortex is able to adapt its contrast response function to match the average local contrast. Here we examine the neuronal mechanism of contrast adaptation by direct intracellular recordings in vivo. Both simple (n = 3) and complex cells (n = 4) show contrast adaptation during intracellular recording. For simple cells, that the amplitude of fluctuations in membrane potential induced by a drifting grating stimulus follows a contrast response relation similar to lateral geniculate relay cells, and does not reflect the high gain and adaptive properties seen in the action potential discharge of the neurons. We found no evidence of significant shunting inhibition that could explain these results. In complex cells there was no change in the mean membrane potential for different contrast stimuli or different states of adaptation, despite marked changes in discharge rate. We use a simplified electronic model to discuss the central features of our results and to explain the disparity between the contrast response functions of the membrane potential and action potential discharge in simple cells.     

Single neurons are differently involved in stimulus-specific oscillations in cat visual cortex

Synchronised oscillatory population events (35-80 Hz; 60-300 ms) can be induced in the visual cortex of cats by specific visual stimulation. The oscillatory events are most prominent in local slow wave field potentials (LFP) and multiple unit spikes (MUA). We investigated how and when single cortical neurons are involved in such oscillatory population events. Simultaneous recordings of single cell spikes, LFP and MUA were made with up to seven microelectrodes. Three states of single cell participation in oscillations were distinguished in spike triggered averages of LFP or MUA from the same electrode: (1) Rhythmic states were characterised by the presence of rhythmicity in single cell spike patterns (35-80 Hz). These rhythms were correlated with LFP and MUA oscillations. (2) Lock-in states lacked rhythmic components in single cell spike patterns, while spikes were phase-coupled with LFP or MUA oscillations. (3) During non-participation states LFP or MUA oscillations were present, but single cell spike trains were neither rhythmic nor phase coupled to these oscillations. Stimulus manipulations (from "optimal" to "suboptimal" for the generation of oscillations) often led to systematic transitions between these states (from rhythmic to lock-in to non-participation). Single cell spike coupling was generally associated with negative peaks in LFP oscillations, irrespective of the cortical separation of single cell and population signals (0-6 mm). Our results suggest that oscillatory cortical population activities are not only supported by local and distant neurons with rhythmic spike patterns, but also by those with irregular patterns in which some spikes occur phase-locked to oscillatory events.     

Activating response codes by stimuli in the neglected visual field.

The ability of 2 patients with a clinical deficit of extinction to process stimuli presented contralaterally to their lesions was tested with 2 variants of the flanker task. The patients saw 2 colored stimuli, 1 of which appeared in the center of the visual field and the other either on the ipsior contralateral side. In the peripheral report task, the patients had to report the color of the peripheral stimulus. In the center report task, the patients had to report the color of the central stimulus. The patients were much slower in the peripheral report task when the target was presented contralaterally to their lesion. By contrast, the responses in the center report task were equally influenced by ipsi- and contralateral flankers. The findings indicate that the patients were not impaired in the perceptual processing or the activation of response codes for contralateral stimuli. Their impairment is related to processes needed for generation of overt responses. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Critical flicker frequency (CFF) in the central and peripheral visual field (author''s transl)

The concentrations of total fatty acids and free cholesterol in the plasma of Ayrshire calves decreased following, but not during, short-term exposure to heat. Lower concentrations of total fatty acids and free cholesterol were maintained on prolonged heat exposure. Blood and plasma volumes were little affected by either short-term or prolonged heat exposure. Haematocrit rose during short-term heat stress and on prolonged heat exposure there was a decrease in erythrocyte fragility.