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M J Hawken

Publications and source records attributed to M J Hawken.

29 records · Page 2Linked to original sources
PubMed1988

Laminar organization and contrast sensitivity of direction-selective cells in the striate cortex of the Old World monkey.

The directional preference of neurons sampled from all layers of the striate cortex was determined using the responses to drifting grating stimuli of optimal spatial and temporal frequency. In addition, contrast sensitivity as a function of spatial frequency was measured and from the resulting spatial contrast sensitivity function the peak contrast sensitivity and optimal spatial frequency were obtained. The distribution of directionally selective cells showed a distinct laminar pattern. Upper layer 4 (4a, 4b, and 4c alpha) and layer 6 were the only cortical layers with neurons that showed a pronounced preference for the direction of stimulus motion. The directionally selective cells in these layers are among those with the highest contrast sensitivities but had optimal spatial frequencies that were confined to the low and middle range of the optimal spatial frequency distribution. These findings suggest that the directionally selective cells may fall into at least 2 distinct populations, which may be the first stages in the visual pathway that correspond to those channels, inferred from psychophysical experiments, that underlie the detection of movement.

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PubMed1987

Spatial properties of neurons in the monkey striate cortex.

Contrast sensitivity as a function of spatial frequency was determined for 138 neurons in the foveal region of primate striate cortex. The accuracy of three models in describing these functions was assessed by the method of least squares. Models based on difference-of-Gaussians (DOG) functions where shown to be superior to those based on the Gabor function or the second differential of a Gaussian. In the most general case of the DOG models, each subregion of a simple cell's receptive field was constructed from a single DOG function. All the models are compatible with the classical observation that the receptive fields of simple cells are made up of spatially discrete 'on' and 'off' regions. Although the DOG-based models have more free parameters, they can account better for the variety of shapes of spatial contrast sensitivity functions observed in cortical cells and, unlike other models, they provide a detailed description of the organization of subregions of the receptive field that is consistent with the physiological constraints imposed by earlier stages in the visual pathway. Despite the fact that the DOG-based models have spatially discrete components, the resulting amplitude spectra in the frequency domain describe complex cells just as well as simple cells. The superiority of the DOG-based models as a primary spatial filter is discussed in relation to popular models of visual processing that use the Gabor function or the second differential of a Gaussian.

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PubMed1984

Contrast sensitivity and orientation selectivity in lamina IV of the striate cortex of Old World monkeys.

Contrast sensitivity and orientation selectivity were measured for neurons in lamina IV of macaque striate cortex. Contrast sensitivity was determined for a range of spatial frequencies, using a staircase method. The stimuli were at the optimal orientation, direction and speed of drift for each neuron. The assignment of each recording site to a subdivision of lamina IV was made by histological reconstruction of each electrode penetration from sections reacted for cytochrome oxidase and stained for Nissl substance. Neurons in the magnocellular recipient zone of IVc (IVc alpha) have high contrast sensitivities, while those in the parvocellular recipient zone (IVc beta) have low contrast sensitivities. Both of the upper subdivisions of lamina IV (IVa and IVb) contain a mixture of neurons with high and low contrast sensitivities. There were orientation selective neurons within all subdivisions of lamina IV, even in IVc, whereas non-oriented neurons were found only in those subdivisions that receive a direct parvocellular geniculate input (IVa and IVc beta).

Animals↗
PubMed1984

The postnatal reduction of the uncrossed projection from the nasal retina in the cat.

We have investigated the postnatal reduction of the uncrossed projection from the nasal retina in the cat by injecting horseradish peroxidase into one optic tract of kittens and cats and retrogradely labeling the cells in the ipsilateral retina that have an uncrossed projection to the brain. The newborn kitten has over 600 uncrossed cells in the nasal retina. The number is reduced to about one-quarter of that value by postnatal day 10. The two adult cats examined had 75 and 100 of these ipsilaterally projecting nasal cells. They are distributed all across the nasal retina, and most have the morphology characteristic of gamma cells. A lesion in one optic tract in the newborn kitten results in an increase in the number of cells from the nasal retina with an ipsilateral projection at maturity. There are more of these cells in the region that has been depleted of ganglion cells by the lesion. This excess consists mostly of gamma and epsilon cells. These findings indicate that competitive factors play a role in the elimination of inappropriate ganglion cell projections in the cat, and that this process contributes to the precision of the nasotemporal division of the retina.

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PubMed1982

Rapid restoration of functional input to the visual cortex of the cat after brief monocular deprivation.

1. We recorded extracellularly from 1045 neurones in area 17 of seven monocularly deprived kittens and we employed careful sampling techniques to examine the effects of removing the signals from the non-deprived eye on the proportion of cells responding to stimulation of the deprived eye.2. Monocular deprivation itself produced a pronounced over-all change in the ocular dominance of neurones in favour of the experienced eye, but both between animals and even between different samples of cells in individual animals there were marked variations in the magnitude of the effect.3. Monocular deprivation starting immediately at the time of natural eye opening and lasting for several weeks reduced to about 10% the proportion of cortical neurones influenced through the deprived eye. Enucleation of the experienced eye did not then produce a significant increase in the proportion of cells responsive to the deprived eye.4. Monocular deprivation lasting 3 days or more and beginning at 5 weeks of age, after normal binocular vision, also shifted ocular dominance substantially: 11-27% of neurones responded through the deprived eye. Enucleation of the experienced eye or topical anaesthesia of the optic nerve resulted in a substantial recovery of input from the deprived eye: up to 78% of the cells responded.5. In such animals the majority of neurones that recovered input from the deprived eye had receptive field properties qualitatively similar to those of normal cortical cells. Recording in a single penetration both before and after enucleation (or optic nerve block) suggested that the orientation preferences of cells with recovered input followed the same sequence as was originally present for the non-deprived eye.6. Recovery of input occurred in all cortical laminae in which cells were recorded, even in layer IV, and mainly took the form of an expansion of already existing clusters of cells driven by the deprived eye.7. Spontaneous activity tended to increase after enucleation.8. The results indicate that monocular deprivation after a period of normal binocular vision leaves subthreshold but functionally organized synaptic input from the deprived eye on cortical cells, which is revealed when activity arising in the retina of the non-deprived eye is abolished.

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PubMed1982

Brief monocular deprivation leaves subthreshold synaptic input on neurones of the cat's visual cortex.

1. We have examined neurones in area 17 of monocularly deprived kittens for subthreshold input in response to visual stimulation through the deprived eye during reversible abolition of activity from the non-deprived eye and during increased excitability of cortical neurones induced by ionophoresis of DL-homocysteic acid (DL-H).2. After two or three days of monocular deprivation, beginning five weeks post-natally, most cortical neurones were dominated by the non-deprived eye. From a sample of forty-three neurones, from three kittens, driven exclusively by the non-deprived eye, only 16% developed responses to stimulation through the deprived eye as a result of reversible pressure blinding of the non-deprived eye. The responses through the deprived eye during pressure blinding usually developed over a period of several minutes and were always transitory: in no cases did the response persist for more than a few minutes after the return of the normal response through the non-deprived eye. Occasionally cells became responsive through the deprived eye during a short period of heightened general excitability after the release of pressure.3. Ionophoretic application of DL-H usually increased the spontaneous activity of cortical neurones. From two kittens monocularly deprived for three days during the fourth or fifth week of life, out of a sample of sixteen cortical neurones initially responsive only through the non-deprived eye, 63% showed responses to visual stimulation through the deprived eye during DL-H application. From a kitten monocularly deprived for 12 d from post-natal day 38, 28% of eighteen initially monocular neurones developed responses through the deprived eye during DL-H application.4. Preliminary results from intracellular recording showed apparently monocular neurones with excitatory input from the deprived eye producing subthreshold synaptic activity in response to moving bars of the same orientation that gave a suprathreshold response through the non-deprived eye.

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PubMed1981

Spatial and temporal properties of cat geniculate neurones after prolonged deprivation.

1. Extracellular recordings were made from the dorsal lateral geniculate nucleus of monocularly deprived, dark-reared and normal cats. The spatial and temporal properties of the neurones were studied. 2. The mean acuity of X-cells with receptive fields 3 degrees of the area centralis was 3.9 c/degree for deprived eye cells from monocularly deprived cats, compared was 3.8 c/degree for normal cells. 3. The mean activity of X-cells with receptive fields within 4 degrees of the area centralis was 4.3 c/degree for a dark-reared cat compared with 4.0 c/degree for a normal cat. 4. The peak response rates of X-cells to their best spatial frequency were determined. The mean values for the normal, monocularly deprived and dark-reared populations were all similar. 5 Measurement of the temporal frequency tuning of a number of cells was made. The mean peak temporal frequency for the dark-reared X-cells was lower than for monocularly deprived or normal X-cells. 6. The results are discussed with reference to the location of the primary neural deficit induced by visual deprivation.

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PubMed1976

The membrane potential of rat diaphragm muscle fibres and the effect of denervation.

1. Resting membrane potentials of rat diaphragm muscles were measured in vitro after previous denervation for 0-10 days. In some experiments denervated muscles were incubated in vitro for 3 hr while in others they were cultured for 15-24 hr to allow adequate exposure to drugs before recording. 2. It was found that resting membrane potentials, within 2-5 mm of the site of nerve section were significantly lower, within 3 hr, than resting membrane potentials measured more than 9 mm away from site of nerve section. This difference could be reduced or abolished by bathing preparations in solutions containing adrenaline (10 muM), noradrenaline (10 muM) or isoprenaline (10 muM) or dibutyryl cyclic AMP (10 muM-0-25 mM in the presence of 2 mM theophylline). Cyclic AMP (0-5 mM) was ineffective. 3. Application of solutions containing dibutyryl cyclic AMP for 3 hr also raised the resting membrane potential of muscles denervated 4-5 days previously. Culture studies showed that this effect was sustained when the time of incubation was 24 hr. 4. Incubating freshly denervated preparations with cycloheximide (22 mug/ml.) or actinomycin D (1 mug/ml.) did not prevent the development of the early (3 hr) fall in resting membrane potential despite a concomitant inhibition of RNA or protein synthesis. Culturing freshly denervated muscles in solutions containing cycloheximide (10 or 25 mug/ml.) which blocked 93% of protein synthesis, did not prevent the expected drop in resting membrane potential after 15 or 24 hr. 5. It was found that exposure to ouabain (1 or 5 mM) produced a rapid (15 min) fall in resting membrane potential in innervated and denervated preparations treated with dibutyryl cyclic AMP but not denervated preparations. After 5 days denervation cyclic AMP levels in muscle were increased by about 40%. 6. It is suggested that upon denervation an electrogenic action of a NA+-pump is blocked and that dibutyryl cyclic AMP and catecholamines are capable of stimulating this pump.

Animals↗
PubMedDate not supplied

Temporal-frequency selectivity in monkey visual cortex.

We investigated the dynamics of neurons in the striate cortex (V1) and the lateral geniculate nucleus (LGN) to study the transformation in temporal-frequency tuning between the LGN and V1. Furthermore, we compared the temporal-frequency tuning of simple with that of complex cells and direction-selective cells with nondirection-selective cells, in order to determine whether there are significant differences in temporal-frequency tuning among distinct functional classes of cells within V1. In addition, we compared the cells in the primary input layers of V1 (4a, 4c alpha, and 4c beta) with cells in the layers that are predominantly second and higher order (2, 3, 4b, 5, and 6). We measured temporal-frequency responses to drifting sinusoidal gratings. For LGN neurons and simple cells, we used the amplitude and phase of the fundamental response. For complex cells, the elevation of impulse rate (F0) to a drifting grating was the response measure. There is significant low-pass filtering between the LGN and the input layers of V1 accompanied by a small, 3-ms increase in visual delay. There is further low-pass filtering between V1 input layers and the second- and higher-order neurons in V1. This results in an average decrease in high cutoff temporal-frequency between the LGN and V1 output layers of about 20 Hz and an increase in average visual latency of about 12-14 ms. One of the most salient results is the increased diversity of the dynamic properties seen in V1 when compared to the cells of the lateral geniculate, possibly reflecting specialization of function among cells in V1. Simple and complex cells had distributions of temporal-frequency tuning properties that were similar to each other. Direction-selective and nondirection-selective cells had similar preferred and high cutoff temporal frequencies, but direction-selective cells were almost exclusively band-pass while nondirection-selective cells distributed equally between band-pass and low-pass categories. Integration time, a measure of visual delay, was about 10 ms longer for V1 than LGN. In V1 there was a relatively broad distribution of integration times from 40-80 ms for simple cells and 60-100 ms for complex cells while in the LGN the distribution was narrower.

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