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Proceedings: A new method of plotting the receptive field profiles of visual cortical neurones using an electronic stimulator
... 0.4) whether moving, flashing on and off, or with squsre-wave modulation of contrast (180 ~ phase shift) at a determined rate. The details of the electronic stimulator have been described elsewhere (Dench et al., 1974). The CRT screen was placed at 50 em from the cat's eyes and the display subtended 10 ~ in diameter. ...
Receptive field properties of cells in area 17 of the visual cortex in the cat have been studied by quantitative methods. The cortical cells were classified as sustained or transient according to their response to a stationary, optimal bar at the receptive field centre, this being analogous to the classification of retinal ganglion cells according to their response to a stationary, optimal spot. Evidence is presented that the sustained/transient classification is independent of the simple/complex classification. Sustained cells of both simple and complex types had spatial frequency tuning curves with a sharp low-frequency cut, whereas transient cells, both simple and complex, had tuning curves with a shallow low-frequency cut, and on average were tuned to lower spatial frequencies than sustained cells. Sustained cells of both simple and complex types, had temporal frequency tuning curves with a shallow low-frequency cut, whereas transient cells had curves with a sharp low-frequency cut, and on average were tuned to higher temporal frequencies than sustained cells. The results indicate that sustained and transient cortical cells retain the spatial and temporal properties of sustained and transient retinal ganglion cells, respectively, and thus the two groups of neurones are organised in parallel throughout the visual system, the sustained channel providing high spatial resolution and the transient channel, high temporal resolution.
... Thus, all cells were studied under monocular viewing conditions. Quantitative measurements of the receptive field properties of each cell encountered were made using a grating stimulator (Dench, Ikeda & Wright, 1974) and the number of cells encountered at each layer of the LGN and their precise receptive field positions were analysed. Any intorsion of the eyes during paralysis, or a small torsional rotation (usually between 2 and 30 of downward rotation) due to the pull on the scleral suture, was assessed and corrected for the receptive field position. ...
1. Recordings of single cells were made in layers A and A1 of the lateral geniculate nucleus of kittens raised with convergent squint in one eye, and morphological studies of cells representing the different parts of the visual fields in these layers were also made from histological sections.2. For the normal eye, cells receiving inputs from the nasal and temporal visual fields were evenly represented up to the periphery, whereas for the squinting eye, no cells which permitted quantitative studies of receptive field properties could be found in the periphery of the nasal field.3. The loss of nasal field, represented by the loss of functional cells in the LGN layer A1 fed by the squinting eye, depended on the severity of the squint. The greater the angle of convergent squint, the greater the loss of nasal field represented by the loss of functional cells.4. The cells fed by the squinting eye's temporal visual field retained their brisk function, although minor modifications in the receptive field organisation were apparent.5. The mean perikaryal size was smaller and the cell-density higher for cells in layers fed by the squinting eye. As found for the functional loss of cells, the shrinkage of perikaryal size and the increase of cell-density was smallest in the zones fed by the temporal visual field, and greatest in the zones fed by the peripheral nasal visual field.6. The functional and morphological changes in the cells in the LGN, which receive inputs from the nasal field of the squinting eye, are attributed to part of the temporal retina being hidden behind the bridge of the nose. It is proposed that this is a consequence of disuse atrophy, due to lack of stimulation during the sensitive period of development.
Different levels of anaesthesia in cats surgically prepared under thiopentone sodium were induced by adding 0.2%, 0.8% and 2.2% halothane to 80% N2O, 19% O2 and 1% CO2 mixture. Properties of visual cortical neurones were investigated under each anaesthetic level. 80% N2O alone produced a combination of slow and fast wave components in the EEG (2nd stage of anaesthesia). Under this condition, many cortical neurones could be classified as sustained or transient on the basis of their firing pattern to a stationary bar, and sharp tuning curves for orientation and spatial frequency could be obtained, the cells having low contrast thresholds. As the halothane concentration was increased, the slow wave component of the EEG increased (3rd stage of anaesthesia), the tuning curves of cortical neurones to orientation and spatial frequency became less sharp, the contrast threshold was raised and classification into sustained and transient neurones became difficult. Finally the neurones became undrivable when the EEG showed continuous, large-amplitude slow waves (4th stage of anaesthesia). Thus findings made during the slow wave EEG patterns cannot reveal the full capabilities of cortical neurones.
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