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PubMed1986

The relationship between the geniculocortical afferents and their cortical target cells during development of the cat's primary visual cortex.

To study the prenatal development of connections between the lateral geniculate nucleus (LGN) and the primary visual cortex in the cat, we have examined the relationship between the position of ingrowing afferents from the LGN and their target cells in cortical layers 4 and 6 at various times during the cat's 65 d gestation period and during the first 3 weeks of postnatal life. In 1 series of experiments, the method of transneuronal transport of intraocularly injected tritiated proline (3H-proline), followed by autoradiography, was used to label the developing geniculocortical pathway. In another series, the tritiated thymidine (3H-thymidine) method was employed to keep track of the cells destined for layers 4 and 6 by labeling them on their birthdates (layer 4: embryonic day (E) 37-43; layer 6: E31-36) (Luskin and Shatz, 1985b) and then charting their locations at subsequent times during development. The results of the 2 sets of experiments were compared at corresponding ages. By E39, many of the cells of cortical layer 6 have completed their migrations and are situated within the cortical plate immediately above the subplate. However, the transneuronal labeling pattern indicates that the geniculocotical afferents have not yet arrived within the vicinity of the future visual cortex, but rather are still en route and confined within the optic radiations of the telencephalon. By E42, a week after the first afferents can be detected in the radiations, substantial transneuronal label is found in the subplate immediately below future visual cortex. However, the overlying cortical plate is free of label. Over the next 2 weeks, geniculocortical axons continue to accumulate in the subplate zone, and, in addition, transneuronal label can be found in the marginal zone. By E55 a faint geniculocortical projection can be detected within the cortical plate, but only within its deeper half (future layers 5 and 6), and even then the major portion of the projection is still confined to the subplate. The absence of a projection to cortical layer 4 at these ages is remarkable in view of the results from our 3H-thymidine experiments, which indicate that by E57 the majority of cells destined to belong to layer 4 have already completed their migrations and assumed positions superficial to the cells of layers 5 and 6. By birth, a substantial geniculocortical projection to cortical layer 4 can be detected in the transneuronal autoradiographs.(ABSTRACT TRUNCATED AT 400 WORDS)

Afferent Pathways↗
PubMed2005

Modulation of phosphene perception during saccadic eye movements: a transcranial magnetic stimulation study of the human visual cortex.

Saccadic suppression allows for perceptual stability during rapid movements of the eyes. One of the neural mechanisms may involve saccade-related modulation of neural activity in the visual cortex. Using the perception of phosphenes induced by transcranial magnetic stimulation (TMS) applied over the visual cortex (VC) as an index of cortical excitability, we sought to determine if VC excitability was modulated at varying times relative to saccade onset. We used two measures of excitability: (1) stimulator intensity required to induce phosphenes in 50% of trials, also called the phosphene threshold (PT), and (2) the subjective intensity of the phosphene. We found that there was no change in PT for different saccade-TMS onset asynchronies while there was an increase in perceived phosphene-intensity near the time of saccade onset (F(7,42) = 4.34, P = 0.001). Contrary to what would be expected from a saccadic suppression model, our results suggest that excitability of the visual cortex is slightly enhanced at the time of saccade onset.

Adult↗
PubMed1997

Disruption of orientation tuning in visual cortex by artificially correlated neuronal activity.

In the primary visual cortex, the development of orientation selectivity is influenced by patterns of neural activity. The introduction of artificially correlated activity into the visual pathway (through synchronous activation of retinal ganglion cell axons in the optic nerve) substantially weakens the orientation selectivity of neurons in superficial and deep cortical layers. This is consistent with activity having an instructive role in shaping cortical neuron receptive field tuning properties.

Action Potentials↗
PubMed2001

Direction selectivity of excitatory and inhibitory neurons in ferret visual cortex.

Direction selectivity is a characteristic feature of neurons in the visual cortex of higher mammals. Excitatory and inhibitory cortical neurons receive different patterns of synaptic connections resulting in different receptive field properties. We have analyzed the direction tuning of excitatory and inhibitory neurons of ferret visual cortex using single unit recordings. Direction tuning was constant among neurons in a vertical column. The majority (> 80%) of excitatory (regular spiking) neurons were direction tuned or direction biased. Fast spiking (inhibitory) neurons were orientation, but only weakly or not direction tuned. This indicates that excitatory and inhibitory neurons have different functions in visual processing and their different integration in thalamocortical and intracortical circuits results in a diversification of receptive field properties.

Action Potentials↗
PubMed2003

The receptive-field organization of simple cells in primary visual cortex of ferrets under natural scene stimulation.

The responses of simple cells in primary visual cortex to sinusoidal gratings can primarily be predicted from their spatial receptive fields, as mapped using spots or bars. Although this quasilinearity is well documented, it is not clear whether it holds for complex natural stimuli. We recorded from simple cells in the primary visual cortex of anesthetized ferrets while stimulating with flashed digitized photographs of natural scenes. We applied standard reverse-correlation methods to quantify the average natural stimulus that invokes a neuronal response. Although these maps cannot be the receptive fields, we find that they still predict the preferred orientation of grating for each cell very well (r = 0.91); they do not predict the spatial-frequency tuning. Using a novel application of the linear reconstruction method called regularized pseudoinverse, we were able to recover high-resolution receptive-field maps from the responses to a relatively small number of natural scenes. These receptive-field maps not only predict the optimum orientation of each cell (r = 0.96) but also the spatial-frequency optimum (r = 0.89); the maps also predict the tuning bandwidths of many cells. Therefore, our first conclusion is that the tuning preferences of the cells are primarily linear and constant across stimulus type. However, when we used these maps to predict the actual responses of the cells to natural scenes, we did find evidence of expansive output nonlinearity and nonlinear influences from outside the classical receptive fields, orientation tuning, and spatial-frequency tuning.

Action Potentials↗
PubMedDate not supplied

[A comparison of the take of embryonic amygdala and visual cortex transplants in the rat brain in connection with the possible compensation of functional disorders].

Transplantation of embryonic (E17-18) visual cortex and amygdala was performed into corresponding damaged areas of the adult rat brain. It was shown in Nissl and Golgi preparations (by comparing qualitative and quantitative findings) that 2-6 months after operation the grafts were successful in case of putting them into the corresponding brain areas (cortex to cortex, or amygdala to amygdala). Graft's integration resulted in a selective increase of dendrite length and ramification towards the area of graft-host interface both in amygdala and visual cortex grafts. In case of inadequate graft-host integration the stratification of the grafted visual cortex could be observed. The structural reorganization of grafted neurones is compared with physiological and behavioural findings during the recovery processes in damaged brain.

Amygdala↗
PubMed2005

Visual cortex activation in late-onset, Braille naive blind individuals: an fMRI study during semantic and phonological tasks with heard words.

Visual cortex activity in the blind has been shown in Braille literate people, which raise the question of whether Braille literacy influences cross-modal reorganization. We used fMRI to examine visual cortex activation during semantic and phonological tasks with auditory presentation of words in two late-onset blind individuals who lacked Braille literacy. Multiple visual cortical regions were activated in the Braille naive individuals. Positive BOLD responses were noted in lower tier visuotopic (e.g., V1, V2, VP, and V3) and several higher tier visual areas (e.g., V4v, V8, and BA 37). Activity was more extensive and cross-correlation magnitudes were greater during the semantic compared to the phonological task. These results with Braille naive individuals plausibly suggest that visual deprivation alone induces visual cortex reorganization. Cross-modal reorganization of lower tier visual areas may be recruited by developing skills in attending to selected non-visual inputs (e.g., Braille literacy, enhanced auditory skills). Such learning might strengthen remote connections with multisensory cortical areas. Of necessity, the Braille naive participants must attend to auditory stimulation for language. We hypothesize that learning to attend to non-visual inputs probably strengthens the remaining active synapses following visual deprivation, and thereby, increases cross-modal activation of lower tier visual areas when performing highly demanding non-visual tasks of which reading Braille is just one example.

Adult↗
PubMed1998

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 naïve 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.

Animals↗
PubMedDate not supplied

Centrifugal and centripetal connections of the cat visual cortex.

In experiments on curarized cats unit responses in the dorsal lateral geniculate body to stimulation of various zones in area 17 of the visual cortex were analyzed. Of all cells tested 69% were found to respond antidromically and 8% orthodromically; in 7.6% of cells IPSPs occurred either after an initial antidromic spike or without it. The velocities of conduction of excitation along the corticopetal fibers of the optic radiation varied from 28 to 4.3 m/sec, but the three commonest groups of fibers had conduction velocities of 28-19, 14-12, and 10-9.5 m/sec. A difference between latent periods of antidromic responses of the same neurons was found to stimulation of different zones of the visual cortex; this indicates that axons of geniculo-cortical fibers split into several branches which form contacts with several neurons in area 17 of the visual cortex. The degree and possible mechanisms of cortical influences on neurons of the lateral geniculate body are discussed.

Animals↗
PubMed1996

Regional and laminar differences in synaptic localization of NMDA receptor subunit NR1 splice variants in rat visual cortex and hippocampus.

Changes in N-methyl-D-aspartate (NMDA) receptor expression may represent a molecular substrate for differences in synaptic plasticity between early postnatal and adult brains (Fox and Zahs [1994] Curr. Opinion Neurobiol. 4:112-119). We have, therefore, examined the regional and laminar distribution of NR1, the essential subunit of the NMDA receptor, in two regions in which synaptic plasticity has been most thoroughly studied: primary visual cortex and hippocampus. To study NR1 expression at the light and electron microscopic levels we have used a new antiserum (NR1-C1; Sheng et al. [1994] Nature 368:144-147) directed against a differentially spliced C-terminal exon ("C1"). The most striking result was that the pattern of NR1-C1 labeling in the adult was more restricted than that of previously published NR1-specific antibodies. Specifically, NR1-C1 did not label cells in the CA3, dentate gyrus or subicular regions of the hippocampus or in layer 4 of the visual cortex. Quantitative ultrastructural analysis revealed that these differences were paralleled by differential expression of NR1-C1 at synapses. In sharp contrast to the pattern in the adult, NR1-C1 immunoreactivity was distributed more widely in the developing brain. At postnatal day 11, NR1-C1 splice variants were expressed in all layers of the visual cortex and in all regions of the hippocampus. The transient expression of NR1-C1 splice variants in layer 4 of visual cortex suggests that NR1-C1 may play a role in determining the critical period for binocular plasticity. Continued expression of NR1-C1 in upper and lower layers of the adult cortex and in CA1 of the hippocampus may provide a substrate for plasticity in corticocortical connections and Schaffer collateral synapses beyond the critical period. In addition to abundant postsynaptic staining, NR1-C1 immunoreactivity was found in a large number of axon terminals in the dorsal subiculum, but in very few terminals in visual cortex. This strongly suggests that presynaptic NMDA receptors play a major role in neuronal processing of hippocampal output through the subiculum, but play a relatively minor role in visual processing.

Alternative Splicing↗
PubMedDate not supplied

Neurochemical compartmentation of monkey and human visual cortex: similarities and variations in calbindin immunoreactivity across species.

The compartmental organization of visual cortical neurons was examined across species of primates by directly comparing the pattern of immunoreactivity for the 28-kD vitamin D-dependent calcium-binding protein (calbindin) in area 17 of squirrel monkeys, macaques, and neurologically normal adult humans. Area 17 of macaques and squirrel monkeys was similar in that somata and processes intensely immunoreactive for calbindin were present in the same layers (II-III, IVB, and V) and in both species formed a well-stained matrix that surrounded the CO-rich puffs in layer III. These intensely calbindin-immunoreactive neurons were identified as subpopulations of GABA-immunoreactive neurons. Among the most obvious differences in the two monkey species was the distribution of calbindin-positive elements outside of layer III: a dense immunostained matrix surrounded the puffs in layers II, IVB, V, and VI of squirrel monkeys but the immunostained neurons adopted no regular pattern outside layer III in macaques. In addition, although somata lightly immunoreactive for calbindin were present in both species, they were much more abundant in squirrel monkeys than macaques. The pattern of calbindin immunostaining in human area 17 resembled that of macaques in forming an intense matrix that surrounded puffs only in layer III, yet also resembled that of squirrel monkeys by including large numbers of light immunoreactive somata. These lightly immunostained somata included a very dense population forming a prominent band in layer IVA of human visual cortex. We conclude that for layer III of primary visual cortex, a similar pattern of neuronal chemistry exists across species of primates which is related to this layer's compartmental organization. Yet for other layers, the expression of calbindin immunoreactivity varies from one species to the next, perhaps reflecting variations in other neuronal properties.

Aged↗
PubMed2003

Distribution and morphological characterization of phosphate-activated glutaminase-immunoreactive neurons in cat visual cortex.

Phosphate-activated glutaminase (PAG) is the major enzyme involved in the synthesis of the excitatory neurotransmitter glutamate in cortical neurons of the mammalian cerebral cortex. In this study, the distribution and morphology of glutamatergic neurons in cat visual cortex was monitored through immunocytochemistry for PAG. We first determined the specificity of the anti-rat brain PAG polyclonal antibody for cat brain PAG. We then examined the laminar expression profile and the phenotype of PAG-immunopositive neurons in area 17 and 18 of cat visual cortex. Neuronal cell bodies with moderate to intense PAG immunoreactivity were distributed throughout cortical layers II-VI and near the border with the white matter of both visual areas. The largest and most intensely labeled cells were mainly restricted to cortical layers III and V. Careful examination of the typology of PAG-immunoreactive cells based on the size and shape of the cell body together with the dendritic pattern indicated that the vast majority of these cells were pyramidal neurons. However, PAG immunoreactivity was also observed in a paucity of non-pyramidal neurons in cortical layers IV and VI of both visual areas. To further characterize the PAG-immunopositive neuronal population we performed double-stainings between PAG and three calcium-binding proteins, parvalbumin, calbindin and calretinin, to determine whether GABAergic non-pyramidal cells can express PAG, and neurofilament protein, a marker for a subset of pyramidal neurons in mammalian neocortex. We here present PAG as a neurochemical marker to map excitatory cortical neurons that use the amino acid glutamate as their neurotransmitter in cat visual cortex.

Animals↗
PubMed1991

Magnetic coil stimulation of human visual cortex: studies of perception.

The effects of magnetic coil (MC) stimulation of human visual cortex on the foveal perception of briefly presented letter trigrams include: (1) letters were nearly always reported correctly at visual stimulus-MC pulse intervals less than 60-80 msec or greater than 120-140 msec. Thus, by 120-140 msec, information related to letter recognition is relayed from calcarine cortex. (2) Presentation of equiluminant chromatic stimuli (specifically green letters against a red background) results in suppression curves which commence at longer latencies than those obtained with achromatic stimuli. (3) At a stimulus-MC pulse interval of 100 msec, shifting the MC laterally or rostrally resulted in suppression of the contralateral or caudal-most letter respectively. This implies a focal, topographical effect on visual cortex. (4) Two trigram stimuli separated in time (e.g. 100 msec) resulted in classical backward masking in which S1 (the target) was suppressed by S2 (the mask), using an S2/S1 luminance-contrast ratio of 4:1. When the MC was subsequently discharged 80-100 msec after S2, and S2 was suppressed, the response to S1 was easily retrieved (unmasked). Presumably, by 160 msec, S1 has been transmitted to the next processing, extrastriate level. (5) The unmasking phenomenon has been used to track information flow from visual cortex to higher cortical centers (e.g. Wernicke's, Broca's, and related areas). (6) Using a prototype repetitive stimulator, a consecutive train of single MC pulses given 70, 143 and 216 msec following a brief alphabetic trigram stimulus elicited a significant reduction in letter perception. This notably contrasts with the absence of suppression when a single MC pulse was given 70 or 143 msec following presentation of the alphabetic trigram. The results with 3 pulses suggest that the first MC pulse (at 70 msec) delays but requires repetition to prevent processing and/or transmission of information from visual cortex.

Electroencephalography↗
PubMed2003

Neuronal correlates of perception in early visual cortex.

We used functional magnetic resonance imaging (fMRI) to measure activity in human early visual cortex (areas V1, V2 and V3) during a challenging contrast-detection task. Subjects attempted to detect the presence of slight contrast increments added to two kinds of background patterns. Behavioral responses were recorded so that the corresponding cortical activity could be grouped into the usual signal detection categories: hits, false alarms, misses and correct rejects. For both kinds of background patterns, the measured cortical activity was retinotopically specific. Hits and false alarms were associated with significantly more cortical activity than were correct rejects and misses. That false alarms evoked more activity than misses indicates that activity in early visual cortex corresponded to the subjects' percepts, rather than to the physically presented stimulus.

Action Potentials↗
PubMed2006

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.

Action Potentials↗
PubMed1991

Paths of information flow through visual cortex.

The main route of information flow in the cerebral cortex is from the middle layers of cortex to upper and lower layers. However, upper layers of the cat primary visual cortex can be directly driven by inputs from secondary visual cortex when activity in middle layers is disrupted. Upper-layer activity can be driven either by middle layers or by direct corticocortical inputs. One consequence of this result is that areas of cortex thought to be carrying out low-order analysis may be able to extract considerable information from higher order areas.

Animals↗
PubMed1999

Conditioned and unconditioned aversive stimuli enhance light-induced fos expression in the primary visual cortex.

Studies in rats indicate that photic responses within the dorsal lateral geniculate nucleus can be enhanced in response to stimuli known to induce negative emotional arousal. Little is known, however, about the effect of such stimuli on photic responses within primary visual cortex, the principal projection area of the dorsal lateral geniculate. Here, we examined the effect of unconditioned and conditioned aversive stimuli on photic responses within the primary visual cortex in rats using expression of the transcription factor Fos as a functional marker of neuronal activation. In previous studies carried out within the circadian visual system, we found that photic induction of Fos within the principal target area of the circadian visual pathway, the suprachiasmatic nucleus of the hypothalamus, was attenuated when the light stimulus was given concurrently with an aversive footshock or was made an aversive conditioned stimulus through previous pairings with footshock. In addition, we found that photic stimulation of Fos expression in the suprachiasmatic nucleus was attenuated in a context made aversive through previous pairings with footshock. We now report that in these same animals, unlike what was seen within the suprachiasmatic nucleus, Fos expression in the primary visual cortex is significantly elevated. These findings support the view that emotional arousal can enhance the response of cells in the visual cortex to photic input, and point to the differential effect of aversive emotional events on photic responses within pathways underlying visual perception and those involved in circadian regulation.

Animals↗
PubMed1991

Mechanisms of inhibition in cat visual cortex.

1. Neurones from layers 2-6 of the cat primary visual cortex were studied using extracellular and intracellular recordings made in vivo. The aim was to identify inhibitory events and determine whether they were associated with small or large (shunting) changes in the input conductance of the neurones. 2. Visual stimulation of subfields of simple receptive fields produced depolarizing or hyperpolarizing potentials that were associated with increased or decreased firing rates respectively. Hyperpolarizing potentials were small, 5 mV or less. In the same neurones, brief electrical stimulation of cortical afferents produced a characteristic sequence of a brief depolarization followed by a long-lasting (200-400 ms) hyperpolarization. 3. During the response to a stationary flashed bar, the synaptic activation increased the input conductance of the neurone by about 5-20%. Conductance changes of similar magnitude were obtained by electrically stimulating the neurone. Neurones stimulated with non-optimal orientations or directions of motion showed little change in input conductance. 4. These data indicate that while visually or electrically induced inhibition can be readily demonstrated in visual cortex, the inhibition is not associated with large sustained conductance changes. Thus a shunting or multiplicative inhibitory mechanism is not the principal mechanism of inhibition.

Action Potentials↗