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At least 1,495 records · Page 83Linked to original sources
PubMed2000

Cross-modal and cross-temporal association in neurons of frontal cortex.

The prefrontal cortex is essential for the temporal integration of sensory information in behavioural and linguistic sequences. Such information is commonly encoded in more than one sense modality, notably sight and sound. Connections from sensory cortices to the prefrontal cortex support its integrative function. Here we present the first evidence that prefrontal cortex cells associate visual and auditory stimuli across time. We gave monkeys the task of remembering a tone of a certain pitch for 10 s and then choosing the colour associated with it. In this task, prefrontal cortex cells responded selectively to tones, and most of them also responded to colours according to the task rule. Thus, their reaction to a tone was correlated with their subsequent reaction to the associated colour. This correlation faltered in trials ending in behavioural error. We conclude that prefrontal cortex neurons are part of integrative networks that represent behaviourally meaningful cross-modal associations. The orderly and timely activation of neurons in such networks is crucial for the temporal transfer of information in the structuring of behaviour, reasoning and language.

Action Potentials↗
PubMed1991

Is colour vision possible with only rods and blue-sensitive cones?

At night all cats are grey, but with the approach of dawn they take on colour. By starlight, a single class of photoreceptors, the rods, function, whereas by daylight, three classes, the blue-, green- and red-sensitive cones, are active and provide colour vision. Only by comparing the rates of quantal absorption in more than one photoreceptor class is colour vision possible. Although the comparisons generally take place between the cones, they can involve the rods as well. Here we investigate the wavelength discrimination of an extremely rare group of individuals, blue-cone monochromats, who have only rods and one class of cones. We find that these individuals can distinguish wavelengths (440 to 500 nm) in the twilight region where the rods and blue-sensitive cones are simultaneously active.

Color Perception↗
PubMed1999

Position of a 'green-red' hybrid gene in the visual pigment array determines colour-vision phenotype.

The X-linked red- and green-pigment genes are arranged in a head-to-tail tandem array. The colour-vision defect of deuteranomaly (in 5% of males of European descent) is associated with a 5'-green-red-3' visual-pigment hybrid gene, which may also exist in males with normal colour vision. To explain why males with a normal red, a normal green and a green-red hybrid gene may have either normal or deutan colour vision, we hypothesized that only the first two genes are expressed and deuteranomaly results only if the green-red hybrid gene occupies the second position and is expressed preferentially over normal green-pigment genes occupying more distal positions. We used long-range PCR amplification and studied 10 deutan males (8 deuteranomalous and 2 deuteranopic) with 3 visual pigment genes (red, green and green-red hybrid) to investigate whether position of the hybrid gene in the array determined gene expression. The green-red hybrid gene was always at the second position (and the first position was always occupied by the red gene). Conversely, in two men with red, green and green-red hybrid genes and normal colour vision, the hybrid gene occupied the third position. When pigment gene mRNA expression was assessed in post-mortem retinae of three men with the red, green and green-red genotype, the green-red hybrid gene was expressed only when located in the second position. We conclude that the green-red hybrid gene will only cause deutan defects when it occupies the second position of the pigment gene array.

Color Perception↗
PubMed1995

Does occupational exposure to argon laser radiation decrease colour contrast sensitivity in UK ophthalmologists?

The objects of the study were to determine: (1) whether United Kingdom ophthalmologists who used argon lasers had the elevation of colour-contrast thresholds previously discovered and (2) whether other users of argon lasers showed any unusual loss of colour vision. A total of 1072 UK ophthalmologists filled in a questionnaire about their professional use of lasers, the length of time spent operating, and their out-of-doors activities. Their colour vision was then tested by a new sensitive system, and if any abnormality was detected, a clinical eye examination was performed. The results were as follows: (1) Colour vision testing was shown to be reliable. Any self-selection bias was excluded. Test-retest variability was small. Normal results did not change during the survey. (2) A number of men with high red-green thresholds were discovered. Some were aware of their congenital insensitivity. The frequency of all such defects was less than the known incidence of congenital colour deficiency in the male population. (3) Additionally a number of high tritan (blue-yellow) thresholds were encountered, some associated with reported diabetes and hypertension. In other cases of this type, undetected or unacknowledged systemic disease may be present. (4) After making allowance for all these incidental causes of loss of colour vision, and for the effect of age on colour vision (which is very small) only four of the sample were > 2 SD above normal. (5) However, the average blue-yellow thresholds of ophthalmologists were slightly and highly significantly raised compared with normal, in the first year of the survey. During the second and third years, the mean thresholds declined to normal. Similar but less significant findings were found for protan thresholds. It is concluded that the enhanced safety precautions recently introduced are associated with a recovery of colour vision in this population, demonstrating that any changes to individuals were reversible. Colour vision screening has proved able to detect mild ocular abnormalities due to systemic and congenital disease.

Adult↗
PubMed1996

Colour vision in diabetic and normal pseudophakes is worse than expected.

Automated colour vision testing in pseudophakes showed unexpected results. Chromatic discrimination sensitivity was measured in 22 diabetic pseudophakes with no retinopathy, 23 diabetic pseudophakes with background retinopathy and 34 non-diabetic pseudophakes. These results were compared with those in age-matched normal and diabetic phakic subjects, all of whom had good vision. The diabetics were also matched for retinopathy grading and duration of diabetes. In all three groups, red-green discrimination sensitivity was worse in the pseudophakes when compared with the corresponding phakic subjects (normals, p < 0.001; no retinopathy, p = 0.467; background retinopathy, p = 0.057). However, tritan vision was marginally worse in the normal pseudophake group but was better in the two diabetic pseudophake groups, when compared with phakic controls. This may be due to a reduction in tritan sensitivity in age-matched phakic controls from the effects of increased lens yellowing with age.

Aged↗