D.N. Spinelli

Visual Experience Modifies Distribution of Horizontally and Vertically Oriented Receptive Fields in Cats

Cats were raised from birth with one eye viewing horizontal lines and one eye viewing vertical lines. Elongated receptive fields of cells in the visual cortex were horizontally or vertically oriented—no oblique fields were found. Units with horizontal fields were activated only by the eye exposed to horizontal lines; units with vertical fields only by the eye exposed to vertical lines.

Modification of the distribution of receptive field orientation in cats by selective visual exposure during development

SummaryA novel procedure was used to rear kittens under conditions of controlled visual experience: one eye was exposed only to vertical lines while the other eye, simultaneously, was exposed only to horizontal lines. Stimuli were presented in a mask which the animals wore whenever they were in a lighted environment. At the conclusion of the rearing period elongated receptive fields of units recorded from the visual cortex of these animals were oriented either horizontally or vertically. This is in contrast to the full complement of receptive field orientations found in normal cats. Furthermore, units with vertically oriented fields were predominantly or exclusively activated by the eye which had been exposed to vertical lines, while neurons with horizontally oriented fields were predominantly or exclusively activated by the eye which had been exposed to horizontal lines. Normally, 80–90% of the neurons in the visual cortex of the cat are activated by both eyes. The consequences of this controlled visual experience provide evidence for highly selective modification of neuronal connectivity by environmental conditions prevailing during development. Sufficient control of the visual environment was achieved to allow direct comparison between single unit response characteristics and the specific stimuli presented during rearing.

Changes in visual recovery functions and unit activity produced by frontal and temporal cortex stimulation

Abstract Chronic electrical stimulation of the frontal cortex of awake monkeys enhanced the recovery functions recorded from electrodes implanted in the striate cortex. The effect is opposite to that obtained when the inferotemporal cortex is stimulated in this fashion. Further, unit activity at cortical and geniculate stations (recorded from cats) was, as a rule, reciprocally influenced by frontal and temporal cortex stimulation. Such a reciprocal effect was not obtained at the optic nerve level where the effects of the cortical stimulation, though marked, were indistinguishable from one another. Observations of the effect of such stimulations on unit activity in the lateral geniculate nucleus suggest that inferotemporal cortex excitation alters the configuration of the receptive field while frontal cortex stimulation influences the background activity of the unit.

Visual experience as a determinant of the response characteristics of cortical receptive fields in cats

SummaryCats reared with their visual world restricted to vertical lines for one eye and horizontal lines for the other had, in their visual cortices, units with elongated receptive fields that were either vertically or horizontally oriented. These receptive fields could be mapped only using that eye which had seen lines of the same orientation during development. Other units had diffuse, unresponsive receptive fields (Hirsch and Spinelli, 1970). Six cats, from the group above, were revived and allowed normal binocular viewing in an attempt to determine the possibility and extent of adding other types of receptive fields by giving other experiences to their visual systems. After exposure to a normal environment for up to 19 months it was found that indeed there had been a massive increase in the percentage of those classes of receptive fields that were either absent or weak at the end of the selective visual experience. Significantly, these receptive fields, acquired during binocular viewing, were very often binocular.The results, however, show that units whose response characteristics mimic the stimuli viewed during development were almost completely unaffected by normal binocular visual experience, i. e., they were monocularly activated and had the orientation appropriate for the stimuli viewed by the eye from which they could be mapped. Most impressive are a few units whose receptive field shape is almost a carbon copy of the pattern viewed during development. The data provide evidence that visual experience has a direct continuing and lasting effect on the functional connectivity of cells in the visual cortex.

Auditory specificity in unit recordings from cat's visual cortex.

Abstract A substantial percentage of cells in the primary visual cortex of the cat can be activated by nonvisual stimuli. Twenty-five cells were studied in detail in five cats and their responses to visual and acoustic stimuli tested. While all units could be activated by visual stimuli, seven of these responded to visual and acoustic stimulation. Analysis with frequency-modulated tones showed that these seven units were responsive to specific parameters of the sound stimuli. Twodimensional maps done with a small disc on a contrasting background showed that these units have, in addition, visual receptive fields.

Centrifugal optic nerve responses evoked by auditory and somatic stimulation

Abstract The evidence for the efferent control of receptor events has recently been repeatedly challenged. The present experiments were undertaken to provide a simple demonstration of the existence of such a mechanism. Clicks were presented to unanesthetized cats and bipolar recordings made of potential changes evoked in the optic nerve and tract with implants of small (300 μ spaced about 0.2 mm) electrode wires. Click initiated optic nerve responses of 10–60 μv amplitude were obtained in fourteen cats at a latency of 20 msec. These responses were unaffected by atropinization or by curarization; they showed amplitude decrement upon repeated presentations and were unobtainable when the animal was restless. They were abolished by bilateral section of the optic tracts central to the implant sites. Similar optic nerve responses could be initiated by tactile stimulation. Also, silent flash produced recordable responses in the eighth cranial nerve. Finally, parametric click-flash interaction effects were observed to differentially affect different fibers in the optic nerve and to alter the B wave of the ERG.

Afferent and efferent activity in single units of the cat's optic nerve.

Abstract Auditory and somatic stimuli have been shown in a previous study to elicit efferent activity in the optic nerve of cats; this activity was recorded with gross electrodes. This study was undertaken with the purpose of identifying efferent activity at the single unit level. Afferent units and the changes induced in their activity by auditory and somatic stimulation were also analyzed. Twenty healthy, adult cats were used; records were taken from 300 units. Twenty-nine of these units were found to be selectively activated by the nonvisual stimuli and classified as efferent. Among the afferent fibers, forty-eight were modified in their activity by auditory and somatic stimulation. Two types of afferent units with characteristics not previously reported for the cats retina were indentified during the course of this work. These were units responsive to the light flux, and units responsive to the direction of movement of a spot of light.

Electrocortical Correlates of Stimulus Response and Reinforcement

Three patterns of electrical response were identified in the occipital cortex of rhesus monkeys making a differential discrimination: an input pattern that identifies which stimulus has been displayed; a reinforcement pattern that indicates whether the outcome of the differential response was rewarded or in error; and an intention pattern that occurs prior to the response and predicts which response the monkey is about to make. Neither the reinforcement nor the intention pattern is present while the monkeys perform at chance; at this time, only the differences due to input can be distinguished. These results suggest that more than simple input transmission is occurring in the primary visual mechanism. The influence of the experience of the organism is apparently encoded in the averaged electrical potentials recorded from the striate cortex.

Changes in visual recovery functions produced by temporal lobe stimulation in monkeys

Abstract The effect of continuous stimulation of the inferotemporal portion of the posterior “association” cortex on potential changes evoked in a primary sensory projection area was studied and changes were found to occur. Further, these changes were found to be restricted to one sensory mode. Lastly, the changes were of such a nature that they permit a model of the action of this system to be suggested.

Visual Receptive Fields in the Cat's Retina: Complications

Visual receptive fields have been mapped with moving patterns in the cats retinal ganglion cells. A small, general-purpose computer was used to collect a matrix of 2500 data points covering a 25�-by-25� region of space. The analysis of 40 units reveals the existence of many nonconcentric receptive fields and also the presence of line and edge detectors.