Critical flicker frequency (CFF) and psychotropic drugs in normal human subjects?A review

Abstract

This literature review presents summary methodological and statistical data on 33 studies in which critical flicker frequency (CFF) thresholds were used to evaluate the effects of acute oral doses of single psychotropic drugs in normal human subjects. In all, 96 drug-dose-study combinations are represented. CFF was found to be altered to a statistically significant degree (P is less than 0.05) in 51 (65%) of the 79 instances in which inferential statistical methods were used to evaluate the results. As expected, stimulants increased CFF while hypnotics decreased it. There is also a discussion of important methodological considerations in the design of psychopharmacological studies employing CFF. While many studies have shown CFF to be sensitive to the effects of psychotropic drugs, there have not always been adequate controls for extraneous factors (especially, set and suggestion, changes in pupillary diameter, and the presence of other commonly used drugs). Finally, consideration is given to the attempts to increase the sensitivity of the CFF test to drug effects.

Critical flicker frequency for quantification of low-grade hepatic encephalopathy

“…36 Determination of Critical Flicker-Fusion Frequency Thresholds. Visual discrimination ability and general arousal were assessed by determination of critical flicker-fusion frequency thresholds 28,31 by using the Schuhfried Test System (Dr. Schuhfried Inc.). 28,[31][32][33] Intrafoveal stimulation with a luminous diode (wave length 650 nm; luminance 270 cd/m 2 ; luminous intensity 5.3 mcd) was achieved through a concave-convex lens system, which allowed eye accommodation to a virtual picture of the light source 12 meters in the distance.…”

“…Psychoactive drugs and caffeine tend to increase and sedatives tend to decrease CFF, as does exhaustive physical exercise. 28,31,[38][39][40][41] Also, antiepileptic drugs can affect CFF, 42 whereas infusion of branched chain amino acids has no effect. 43 Thus, medication has to be considered in the interpretation of CFF data.…”

“…Such tests have not yet been applied to HE patients, but there is a long-standing experience with the flicker-fusion frequency analysis in cerebro-organic syndromes, 28 multiple sclerosis, 29 Alzheimer's disease, 30 and the testing of psychoactive drugs. 31 Current evidence suggests that flicker-fusion frequency analysis reflects not only the efficiency of the visual apparatus, but also the functional efficiency of the cerebral cortex (i.e., general arousal). 28,31 The present data show that critical flicker frequency is a sensitive and objective parameter, which allows quantification of low-grade HE and its short-and long-term evolution.…”

“…31 Current evidence suggests that flicker-fusion frequency analysis reflects not only the efficiency of the visual apparatus, but also the functional efficiency of the cerebral cortex (i.e., general arousal). 28,31 The present data show that critical flicker frequency is a sensitive and objective parameter, which allows quantification of low-grade HE and its short-and long-term evolution.…”

Interaction of H2‐receptor antagonists and benzodiazepine sedation

“…The score used was the mean of three ascending and three descending trials and is expressed in Hz. This test is widely thought to be an objective measure of cortical arousal [21,22].…”