Decrease In Implicit Time Research Articles

Effects of Physical Effort on Neuroretinal Function in Athletes and Non-Athletes: An Electroretinographic Study

Physical exertion may disturb retinal function. We wondered whether different levels of physical performance could affect the plot of neuroretinal activity after dynamic exercise in healthy subjects. The aim of our study was to estimate the effect of increasing intensity physical exercise on retinal activity in 2 groups: athletes (n=10) and non-athletes (n=10). We analyzed the amplitude and implicit time of b-wave electroretinogram (ERG) responses for a photopic white 30-Hz flicker stimulus. Using a cycloergometer, 3 10-minute effort tests with increasing intensity were performed. Each participant was attributed an individual workload value (W) below his lactate threshold (40% VO2max), at his lactate threshold (65%-75% VO2max), and above his lactate threshold (80% VO2max). Five ERG recordings were taken: before the efforts (first), immediately after the 3 consecutive efforts (second to fourth), and 1 hour after the last effort (fifth). After the first effort, in both groups we observed a statistically significant increase in b-wave amplitude (p<0.05), and in non-athletes a decrease in implicit time of b-wave (p<0.05). After the last effort, we observed a decreased b-wave amplitude in non-athletes, whereas in athletes the amplitude remained at a high level. Physical effort significantly differentiated the plot of b-wave amplitude changes between athletes and non-athletes. These findings suggest that strenuous physical effort may disturb signal transfer in the inner retinal layer in non-athletic subjects. The ERGs may be used as a neurophysiologic indicator in defining the cardiovascular training status of an athlete.

Light adaptation, rods, and the human cone flicker ERG.

During the course of light adaptation, the amplitude and implicit time of the human cone ERG change systematically. In the present study, the effect of adapting field luminance on these ERG changes was assessed, and the hypothesis that light adaptation of the rod system is the primary determining factor was evaluated. Cone ERG responses, isolated through the use of 31.1-Hz flicker, were obtained from two visually normal subjects, initially under dark-adapted conditions and then repeatedly for 30 min following the onset of each of a series of ganzfeld adapting fields with luminances that ranged from -1.2 to 2.1 log cd/m2. The increase in flicker ERG amplitude and decrease in implicit time during light adaptation were greatest at the highest adapting field luminances. Photopically equivalent achromatic and long-wavelength adapting fields induced comparable increases in flicker ERG amplitude, while scotopically equivalent adapting fields had considerably different effects. This latter finding demonstrates that the rod system is not a major determinant of the adaptation-induced increase in cone ERG amplitude.

Neural effects of body inversion: photopic oscillatory potentials.

The effect of alterations in retinal and choroidal circulation resulting from changes in body orientation were examined in 10 subjects with normal systemic and intraocular pressures. Body inversion resulted in an increase in the intraocular pressure with a concomitant increase in the ocular perfusion pressure. The effect of these pressure elevations was assessed by photopic oscillatory potentials (OPs). The trends in the change in OP amplitude with experimentally elevated ocular perfusion pressure varied across OP wavelets. OP-1 and the OP index exhibited a statistically significant decrease with an increase in ocular perfusion pressure, with OP-2 to OP-5 showing statistically insignificant reductions. Only OP-5 showed a significant decrease in implicit time with increased perfusion pressure. The magnitude of these changes were quite small despite a greater than 70% increase in the ocular perfusion pressure. Vascular autoregulatory mechanisms are hypothesized to be responsible for maintaining the OPs to within clinically normal levels.

High-frequency VEP wavelets in early infancy: A preliminary study

The flash-evoked visual evoked potential (VEP) was recorded in 12 infants 0–12 weeks of age. Along with traditional low-frequency waves (1–35 Hz), high-frequency (50–100 Hz) wavelets were examined. No wavelets were apparent in records obtained from infants below 4 weeks of age, although the low-frequency waves were clearly present at all ages tested. Wavelets showed a steady increase in amplitude and a small decrease in implicit time across the time period studied. The changes in wavelet development can be interpreted as a reflection of the significant postnatal maturation of the primary visual system, particularly the maculo and visual cortex.