Biomedical subjects

S Cone

Publications and source records attributed to S Cone.

5 recordsLinked to original sources

PubMed1989

Electroretinograms to checkerboard pattern reversal in cats: physiological characteristics and effect of retrograde degeneration of ganglion cells.

Pattern electroretinograms (P-ERGs) evoked by alternating checks were studied in cats. Spatial frequency functions for transient and steady-state P-ERG waves showed a bimodal distribution with a preferred frequency at 0.6-0.75 c/deg and a second amplitude increase at frequencies lower than 0.5 c/deg. Decreasing the pattern luminance by 0.5 log units produced a shift of the spatial tuning curve toward lower spatial frequencies. No temporal tuning was noted in the temporal frequency functions. The bimodal distribution suggests that at spatial frequencies higher than 0.5 c/deg, the tuning reflects a 'contrast response' originating in cells with center surround organization. At spatial frequencies below 0.5 c/deg, the 'luminance response' becomes predominant and is generated in cells sensitive to mean luminance changes. Transient and steady-state P-ERGs to medium and high spatial frequencies were abolished by section of the optic nerve, while low spatial frequency stimuli at or below 0.3 c/deg continued to evoke P-ERGs at 1, 5 and 10 months after surgery. Quantitative whole mount retina microscopic examination confirmed the retrograde degeneration of the ganglion cells. It is concluded that both transient and steady-state P-ERGs to small and medium spatial frequencies checks are predominantly related to ganglion cell activity, while P-ERGs to low spatial frequencies reflect preganglionic cell activity.

Animals↗

PubMed1987

Effects of age and sex on pattern electroretinograms and visual evoked potentials.

Pattern-electroretinograms (P-ERGs) and visual evoked potentials (VEPs) were simultaneously recorded in 112 normal individuals aged 20-75. Two-sized checks subtending 15' and 31' were used as stimuli. A weighted regression analysis was used to determine which of the variables, sex or age, was significant. The latency of the a and b wave of the P-ERGs showed a progressive increase with age but no difference between sexes. The effect was statistically significant for both 15' and 31' checks. There was no statistically significant aging effect for VEPs elicited by 31' checks. Aging, however, affected N70, P100, and the interpeak interval between b wave to N70 and b wave to P100 for responses to 15' checks. Shorter VEP latencies were noted in females for both 15' and 31' checks. The simultaneous recording of P-ERGs and VEPs has demonstrated that aging is a major variable at the retinal level. The effects on the a and b waves are mostly due to optic changes with aging and only partially to aging changes in the neuronal retinal circuitry. The effect of aging on VEPs is different for different size stimuli. The cause is a random neuronal cell loss in the visual pathways from the optic nerve to the visual cortex as the individual ages. The difference in VEP data between sexes may be related to anatomical size and hormonal influences.

Adult↗

PubMed1987

Caffeine and tremor.

Two percent of normal controls noted that drinking coffee made their hands shaky. Eight percent of essential tremor and 6% of Parkinson's disease patients thought that coffee worsened their tremor. In formal tests, a single oral dose of caffeine (325 mg) did not increase physiologic, essential tremor, or parkinsonian tremor at 1, 2, or 3 hours after ingestion. Caffeine only infrequently induces tremor in normal people, and it does not exacerbate pathologic tremor.

Caffeine↗

PubMed1986

Clonidine in the treatment of essential tremor.

The effect of clonidine treatment (average dose 0.4 mg/day) was investigated in 10 patients with essential tremor in a double-blind placebo-controlled design. Tremor amplitude and frequency were recorded with an accelerometer. Tremor was not significantly altered by clonidine therapy. Side effects were common. It is concluded that clonidine is not effective treatment for essential tremor.

Clinical Trials as Topic↗

PubMed1986

Disability in essential tremor: effect of treatment.

We studied 18 patients with essential tremor for difficulty with handwriting, drinking, eating, fine manipulations, and embarrassment. Propranolol and primidone reduced the amplitude of both postural and kinetic tremor. Handwriting, drinking, and eating were improved with therapy, but fine manipulations and motor performance on tapping and pegboard tests were unaltered. Embarrassment remained unchanged. Essential tremor is not a benign condition; disability can be only partly reversed with drug therapy.

Aged↗