Lowered frequency and impaired modulation of gamma band oscillations in a bimodal attention task are associated with reduced critical flicker frequency.

Visual attention is associated with occipital gamma band activity. While gamma band power can be modulated by attention, the frequency of gamma band activity is known to decrease with age. The present study tested the hypothesis that reduced visual attention is associated with a change in induced gamma band activity. To this end, 26 patients with liver cirrhosis and 8 healthy controls were tested. A subset of patients showed symptoms of hepatic encephalopathy (HE), a frequent neuropsychiatric complication in liver disease, which comprises a gradual increase of cognitive dysfunction including attention deficits. All participants completed a behavioral task requiring shifts of attention between simultaneously presented visual and auditory stimuli. Brain activity was recorded using magnetoencephalography (MEG). The individual critical flicker frequency (CFF) was assessed as it is known to reliably reflect the severity of HE. Results showed correlations of behavioral data and HE severity, as indexed by CFF. Individual visual gamma band peak frequencies correlated positively with the CFF (r=0.41). Only participants with normal, but not with pathological CFF values showed a modulation of gamma band power with attention. The present results suggest that CFF and attentional performance are related. Moreover, a tight relation between the CFF and occipital gamma band activity both in frequency and power is shown. Thus, the present study provides evidence that a reduced CFF in HE, a disease associated with attention deficits, is closely linked to a slowing of gamma band activity and impaired modulation of gamma band power in a bimodal attention task.

Influence of saffron supplementation on retinal flicker sensitivity in early age-related macular degeneration.

PURPOSE: To evaluate the functional effect of short-term supplementation of saffron, a spice containing the antioxidant carotenoids crocin and crocetin, in early age-related macular degeneration (AMD). METHODS: Twenty-five patients with AMD were randomly assigned to oral saffron 20 mg/d or placebo supplementation over a 3-month period and then reverted to placebo or saffron for a further 3 months. Focal electroretinograms (fERGs) and clinical findings were recorded at baseline and after 3 months of saffron or placebo supplementation. fERGs were recorded in response to a sinusoidally modulated (41 Hz), uniform field presented to the macular region (18°) at different modulations between 16.5% and 93.5%. Main outcome measures were fERG amplitude (in microvolts), phase (in degrees), and modulation thresholds. RESULTS: After saffron, patients' fERGs were increased in amplitude, compared with either baseline or values found after placebo supplementation (mean change after saffron, 0.25 log µV; mean change after placebo, -0.003 log µV; P < 0.01). fERG thresholds were decreased after saffron supplementation but not placebo, compared with baseline (mean change after saffron, -0.26 log units; mean change after placebo, 0.0003 log units). CONCLUSIONS: The results indicate that short-term saffron supplementation improves retinal flicker sensitivity in early AMD. Although the results must be further replicated and the clinical significance is yet to be evaluated, they provide important clues that nutritional carotenoids may affect AMD in novel and unexpected ways, possibly beyond their antioxidant properties. (ClinicalTrials.gov number, NCT00951288.).

A comparison of two methods for assessing critical flicker fusion frequency in hens.

This paper compared two general methods for assessing critical fusion frequency in hens (gallus gallus domesticus). The first method was a conditional discrimination procedure with the stimuli presented successively. The second was a two-alternative forced-choice procedure with the stimuli presented simultaneously. It was found that both methods of stimulus presentation gave comparable results suggesting that either method is useful when investigating psychophysics in animals. The results also show that hens' critical fusion frequency is considerably higher than that of humans which may account for hens' inability to recognise images presented on standard computer or television monitors.

Priority of face perception during subliminal stimulation using a new color-opponent flicker stimulation.

We developed a new method of color-opponent flicker (COF) stimulation, and investigated behavioral responses for object discrimination at the around threshold frequency of COF stimulation. Pairs of figures, a face, flower, the letter "G" and a random pattern, were drawn with a red and green checkerboard with a black mesh. COF stimulation was produced by presenting pairs of figures alternately (red-green-red-green-) at various frequencies (30-120 Hz). A discrimination task for objects during COF stimulation was performed by 16 healthy subjects. Threshold frequency of COF stimulation was between 50 and 75 Hz. The accuracy rate for face discrimination was significantly higher than those for other objects (p<0.01, ANOVA with Fisher's PLSD multiple comparisons test). The present COF stimulation technique could be useful to investigate subliminal processes of the visual system, and the present results indicate a higher sensitivity and selectivity for face discrimination than those for other objects.

Differential patterns of multisensory interactions in core and belt areas of human auditory cortex.

The auditory cortex is anatomically segregated into a central core and a peripheral belt region, which exhibit differences in preference to bandpassed noise and in temporal patterns of response to acoustic stimuli. While it has been shown that visual stimuli can modify response magnitude in auditory cortex, little is known about differential patterns of multisensory interactions in core and belt. Here, we used functional magnetic resonance imaging and examined the influence of a short visual stimulus presented prior to acoustic stimulation on the spatial pattern of blood oxygen level-dependent signal response in auditory cortex. Consistent with crossmodal inhibition, the light produced a suppression of signal response in a cortical region corresponding to the core. In the surrounding areas corresponding to the belt regions, however, we found an inverse modulation with an increasing signal in centrifugal direction. Our data suggest that crossmodal effects are differentially modulated according to the hierarchical core-belt organization of auditory cortex.

Enhanced and diminished visuo-spatial information processing in autism depends on stimulus complexity.

Visuo-perceptual processing in autism is characterized by intact or enhanced performance on static spatial tasks and inferior performance on dynamic tasks, suggesting a deficit of dorsal visual stream processing in autism. However, previous findings by Bertone et al. indicate that neuro-integrative mechanisms used to detect complex motion, rather than motion perception per se, may be impaired in autism. We present here the first demonstration of concurrent enhanced and decreased performance in autism on the same visuo-spatial static task, wherein the only factor dichotomizing performance was the neural complexity required to discriminate grating orientation. The ability of persons with autism was found to be superior for identifying the orientation of simple, luminance-defined (or first-order) gratings but inferior for complex, texture-defined (or second-order) gratings. Using a flicker contrast sensitivity task, we demonstrated that this finding is probably not due to abnormal information processing at a sub-cortical level (magnocellular and parvocellular functioning). Together, these findings are interpreted as a clear indication of altered low-level perceptual information processing in autism, and confirm that the deficits and assets observed in autistic visual perception are contingent on the complexity of the neural network required to process a given type of visual stimulus. We suggest that atypical neural connectivity, resulting in enhanced lateral inhibition, may account for both enhanced and decreased low-level information processing in autism.

Effects of quetiapine and haloperidol on prepulse inhibition of the acoustic startle (eyeblink) response and the N1/P2 auditory evoked response in man.

Contraction of the orbicularis oculi muscle in response to a sudden loud sound (acoustic startle response) and the N1/P2 component of the auditory evoked potential are both attenuated when a brief low-intensity stimulus is presented 30-500 ms before the 'startle-eliciting' stimulus (PPI). Here, we report the effects of the 'atypical' antipsychotic drug quetiapine and the 'conventional' antipsychotic haloperidol on these responses. Sixteen males (aged 19-38 years) participated in four sessions at 7-day intervals, in which they received quetiapine 12.5 mg, quetiapine 25 mg, haloperidol 3 mg and placebo, according to a balanced double-blind design. Electromyographic (EMG) responses of the orbicularis oculi muscle and N1/P2 auditory evoked potentials were recorded in a 20-min session, 2 h after treatment. Subjects received 40 trials in which 1-kHz sounds were presented: (i) 40 ms, 115 dB ('pulse alone' trials) and (ii) 40 ms, 85 dB, followed after 120 ms by 40 ms, 115 dB ('prepulse/pulse' trials). Mean amplitudes of the EMG response and the N1/P2 potential were derived from the pulse-alone trials and, in each case, percentage PPI was calculated. Serum prolactin was measured after each treatment, and autonomic (heart rate, blood pressure, salivation) and psychological (visual analogue self-ratings of mood and alertness, critical flicker fusion frequency) measures were taken before and after each treatment. Quetiapine 12.5 mg and 25 mg significantly reduced the amplitude of the EMG response without altering its inhibition by prepulses; haloperidol had no effect on EMG response amplitude or PPI. Neither drug affected N1/P2 amplitude or PPI of this response. Quetiapine, but not haloperidol, reduced subjective alertness and critical flicker fusion frequency. Haloperidol, but not quetiapine, elevated serum prolactin level. The ability of quetiapine to attenuate the startle response may reflect its sedative action.

Effects of taurine supplementation on VDT work induced visual stress.

In order to evaluate the effects of dietary taurine supplementation on visual fatigue induced by visual display terminals (VDT) work, 25 male college students aged from 20 to 24 years who were not engaged in VDT work were selected to participate in the study. Volunteers were randomly assigned to either the taurine supplementation (n=13) or the placebo supplementation control group (n=12). Before and after 12 days of taurine (3 g/day) or placebo supplementation, two identical 2.5-hr VDT work tests were performed while recording the P100, N75 and N145 latencies and P100 amplitude of pattern visual evoked potential (PVEP) and the frequency of critical flicker fusion (CFF). Following 2.5-hr of VDT work, the P100 and N75 latencies of PVEP increased ( P<0.01) while the P100 amplitude decreased significantly ( P<0.01). The frequency of CFF also reduced significantly ( P<0.01). After 12 days of taurine supplementation, the reduction in P100 amplitude after VDT work alleviated significantly ( P<0.05). The results suggest that taurine supplementation alleviates visual fatigue induced by VDT work.

The biological week and broader time structures (chronomes): in memory of Gunther Hildebrandt.

Data illustrating the biological week and chronomes are presented in recognition of extensive work of G. Hildebrandt.

Effect of dysoxia and moderate air-hyperbarism on red-green color sensitivity.

The effect of acute air-hyperbarism (maximal 520 kPa), normobaric low and high FIO2 levels (minimal 0.1, maximal 1.0) and hyperbaric oxygen (HBO2) on the red-green sensitivity ratio (rgSR) and on color discrimination for foveal vision were studied. Effects were quantified by measuring the red-green flicker (16 Hz) fusion point for normals with the Oscar tester (Am J Optom Physiol Opt 1983; 60:892-901). Color discrimination was examined with the Lanthony's Desaturated 15 Hue test After 15-20 min of exposure rgSR is enhanced 4% (relatively increased red sensitivity) by normobaric acute hypoxia, and reduced 4% by normobaric hyperoxia (FIO2 = 1.0), but HBO2 gives a smaller reduction, and air-hyperbarism (FIO2 = 0.21) has no effect. Hypercapnia (increased FICO2), normobaric hypoxia (reduced FIO2), and HBO2 increase the duration of the Lanthony's test about 20-40%, but the number of errors were practically unchanged. The reduced effect during HBO2 upon rgSR is attributed to an opposing effect of hypercapnia. The absence of an effect during air-hyperbarism is probably due to a suppression by nitrogen of the effect of high PO2. In general, during moderate air-hyperbarism and HBO2 color vision seems to be normal, but evaluation of the colored scene is probably less stable and slightly slower.

Progressive increase in critical flicker fusion frequency following yoga training.

The critical flicker fusion frequency (CFF) is the frequency at which a flickering stimulus is perceived to be steady, with higher values suggesting greater perceptual accuracy. The CFF was measured in two age-matched groups of healthy male volunteers whose ages ranged from 25 to 39 years, with 18 subjects in each group. After baseline assessments one group (yoga group) received yoga training, while the other group (control group) carried on with their routine activities. Yoga practices included asanas, pranayamas, kriyas, meditation, devotional sessions and lectures on the theory of yoga. After 10 days neither group showed a change in CFF. However, at 20 and at 30 days the yoga group showed significant increases in CFF by 11.1% and 14.9%, respectively (two factor ANOVA, Tukey multiple comparison test). The control group showed no change at the day 20 and day 30 followup.

Sensory perception in uremic patients.

Peripheral (PNS) and central (CNS) sensory nervous system function was quantitatively assessed using neuroselective transcutaneous electrical nerve stimulation (TENS) in a population of 19 chronic hemodialysis patients (ages 17-77, median 47 years; duration 1-14, median 3 years). Cutaneous current perception threshold (CPT) provided an index of PNS integrity, and a new technique involving cranial TENS to characterize cephalic evoked noncutaneous sensations (CENS) was used to assess CNS sensory function. Patients showed both CPT (32%) and CENS (89%) abnormalities as compared with previously tested healthy subjects. No significant correlation was observed between age, duration of dialysis, PNS, and CNS abnormalities. The CPT examination provides a sensitive and easy to administer test of PNS sensory function for the purpose of assessing the adequacy of dialysis in chronic hemodialysis patients; the CENS examination also may prove useful in this regard.

Peripheral field stimulation affects foveal flicker, but not color, sensitivity.

Human observers have different thresholds for flicker detection and color detection of a rapidly flickering spectral stimulus presented on a steady white background. A flickering surround, which did not overlap the stimulus or background, reduced flicker sensitivity but not color sensitivity for both monocular and binocular viewing. However, a flickering surround presented to one eye had no influence upon either color or flicker thresholds of the other eye.