Acute caffeine ingestion affects surround suppression of perceived contrast

Measuring the effects of age on foveal surround suppression of contrast

PURPOSE

The apparent contrast of a visible central grating can be reduced by the presence of a surrounding grating-an effect known as surround suppression of contrast. Surround suppression is strong when the orientation of the surround matches that of the central probe and is strongest in the periphery. There is evidence that surround suppression at the fovea increases in strength with age, and that the orientation dependence of surround suppression is weakened. However, the range of visual stimuli that can produce this effect (and the implicated underlying mechanisms) requires further examination. This study aimed to characterise surround suppression at the fovea and its dependence on age. Visual stimuli with previously unexplored spatiotemporal parameters were used, designed to minimise contributions from spatially short-range overlay masking and temporally transient masking mechanisms.

METHODS

In 20 younger (<30 years) and 17 older (>60 years) observers, psychophysical contrast-matching thresholds were measured using stimuli centred on the fovea. Grating stimuli were presented with either no surround, a collinearly oriented surround or an orthogonally oriented surround. Using a staircase procedure, observers matched the contrast of these central target stimuli to the contrast of a separate reference stimulus. The points of subjective equality between target and reference stimuli were compared between the two surround orientations and between younger and older age groups.

RESULTS

Across all observers, weak foveal surround suppression was found that had little orientation tuning. No evidence for the strength of surround suppression increasing with age is reported.

CONCLUSIONS

These findings suggest that the age-related effects of surround suppression may be dependent on the spatiotemporal parameters of the stimulus used and encourage further exploration of the contrast masking mechanisms affected by age. The mild and weakly orientation-tuned suppression may have been produced by a weak and temporally sustained suppression mechanism.

Impact of coffee intake on human aging: Epidemiology and cellular mechanisms

The conception of coffee consumption has undergone a profound modification, evolving from a noxious habit into a safe lifestyle actually preserving human health. The last 20 years also provided strikingly consistent epidemiological evidence showing that the regular consumption of moderate doses of coffee attenuates all-cause mortality, an effect observed in over 50 studies in different geographic regions and different ethnicities. Coffee intake attenuates the major causes of mortality, dampening cardiovascular-, cerebrovascular-, cancer- and respiratory diseases-associated mortality, as well as some of the major causes of functional deterioration in the elderly such as loss of memory, depression and frailty. The amplitude of the benefit seems discrete (17 % reduction) but nonetheless corresponds to an average increase in healthspan of 1.8 years of lifetime. This review explores evidence from studies in humans and human tissues supporting an ability of coffee and of its main components (caffeine and chlorogenic acids) to preserve the main biological mechanisms responsible for the aging process, namely genomic instability, macromolecular damage, metabolic and proteostatic impairments with particularly robust effects on the control of stress adaptation and inflammation and unclear effects on stem cells and regeneration. Further studies are required to detail these mechanistic benefits in aged individuals, which may offer new insights into understanding of the biology of aging and the development of new senostatic strategies. Additionally, the safety of this lifestyle factor in the elderly prompts a renewed attention to recommending the maintenance of coffee consumption throughout life as a healthy lifestyle and to further exploring who gets the greater benefit with what schedules of which particular types and doses of coffee.

Concurrent consumption of cocoa flavanols and caffeine does not acutely modulate working memory and attention

PURPOSE

Consumption of cocoa flavanols and caffeine might acutely enhance cognition, particularly in synergy. Due to the use of multifaceted tasks in prior research, it is unclear precisely which cognitive functions are implicated. Here we aimed to assess the acute effects of the (joint) ingestion of cocoa flavanols and caffeine on temporal attention, spatial attention, and working memory.

METHODS

In four separate sessions of a randomized, double-blind, placebo-controlled, crossover trial, 48 young adult participants consumed a placebo drink, a cocoa flavanols (415 mg) drink, a caffeine (215 mg) drink, and a drink containing both concurrently. In each session, after ingestion, we tested performance in three cognitive tasks. We tested temporal attention in a dual-target rapid serial visual presentation paradigm, known to elicit the attentional blink, in which the time between the targets was manipulated. We measured spatial attention in a visual search task, where we varied the number of distractors that appeared simultaneously with the target. We tested working memory in a delayed recall task, in which the number of stimuli to be remembered was manipulated.

RESULTS

We obtained the expected performance pattern in each task, but found no evidence for modulation of response accuracy or reaction times by the ingestion of either substance, nor of their combined ingestion, even in the most challenging task conditions.

CONCLUSIONS

We conclude that, even when jointly ingested, neither the tested amount of cocoa flavanols nor caffeine have acute effects that are robustly measurable on cognitive tasks that target attention and working memory specifically.

Enhanced visual contrast suppression during peak psilocybin effects: Psychophysical results from a pilot randomized controlled trial

In visual perception, an effect known as surround suppression occurs wherein the apparent contrast of a center stimulus is reduced when it is presented within a higher-contrast surrounding stimulus. Many key aspects of visual perception involve surround suppression, yet the neuromodulatory processes involved remain unclear. Psilocybin is a serotonergic psychedelic compound known for its robust effects on visual perception, particularly texture, color, object, and motion perception. We asked whether surround suppression is altered under peak effects of psilocybin. Using a contrast-matching task with different center-surround stimulus configurations, we measured surround suppression after 25 mg of psilocybin compared with placebo (100 mg niacin). Data on harms were collected, and no serious adverse events were reported. After taking psilocybin, participants (n = 6) reported stronger surround suppression of perceived contrast compared to placebo. Furthermore, we found that the intensity of subjective psychedelic visuals induced by psilocybin correlated positively with the magnitude of surround suppression. We note the potential relevance of our findings for the field of psychiatry, given that studies have demonstrated weakened visual surround suppression in both major depressive disorder and schizophrenia. Our findings are thus relevant to understanding the visual effects of psilocybin, and the potential mechanisms of visual disruption in mental health disorders.

Short-term homeostatic visual neuroplasticity in adolescents after two hours of monocular deprivation

In healthy adults with normal vision, temporary deprivation of one eye's visual experience produces transient yet robust homeostatic plasticity effects, where the deprived eye becomes more dominant. This shift in ocular dominance is short-lived and compensatory. Previous work shows that monocular deprivation decreases resting state gamma aminobutyric acid (GABA; inhibitory neurotransmitter) levels in visual cortex, and that those with the greatest reduction in GABA have stronger shifts due to monocular deprivation. Components of the GABAergic system in visual cortex vary with age (early childhood, early teen years, ageing); hence if GABA is critical to homeostatic plasticity within the visual system, adolescence may be a key developmental period where differences in plasticity manifest. Here we measured short-term visual deprivation effects on binocular rivalry in 24 adolescents (aged 10-15 years) and 23 young adults (aged 20-25 years). Despite differences in baseline features of binocular rivalry (adolescents showed more mixed percept p < 0.001 and a tendency for faster switching p = 0.06 compared to adults), deprived eye dominance increased (p = 0.01) similarly for adolescents and adults after two hours of patching. Other aspects of binocular rivalry - time to first switch (heralding the onset of rivalry) and mixed percept - were unaltered by patching. These findings suggest that binocular rivalry after patching can be used as a behavioral proxy for experience-dependent visual cortical plasticity in adolescents in the same way as adults, and that homeostatic plasticity to compensate for temporarily reduced visual input is established and effective by adolescence.

Confounding effects of caffeine on neuroplasticity induced by transcranial alternating current stimulation and paired associative stimulation

OBJECTIVE

We examined the effects of caffeine, time of day, and alertness fluctuation on plasticity effects after transcranial alternating current stimulation (tACS) or 25 ms paired associative stimulation (PAS25) in caffeine-naïve and caffeine-adapted subjects.

METHODS

In two randomised, double-blinded, cross-over or placebo-controlled (caffeine) studies, we measured sixty subjects in eight sessions (n = 30, Male: Female = 1:1 in each study).

RESULTS

We found caffeine increased motor cortex excitability in caffeine naïve subjects. The aftereffects in caffeine naïve subjects were enhanced and prolonged when combined with PAS 25. Caffeine also increased alertness and the motor evoked potentials (MEPs) were reduced under light deprivation in caffeine consumers both with and without caffeine. In caffeine consumers, the time of day had no effect on tACS-induced plasticity.

CONCLUSIONS

We conclude that caffeine should be avoided or controlled as confounding factor for brain stimulation protocols. It is also important to keep the brightness constant in all sessions and study groups should not be mixed with caffeine-naïve and caffeine consuming participants.

SIGNIFICANCE

Caffeine is one of the confounding factors in the plasticity induction studies and it induces different excitability effects in caffeine-naïve and caffeine-adapted subjects. This study was registered in the ClinicalTrials.gov with these registration IDs: 1) NCT03720665 https://clinicaltrials.gov/ct2/results?cond=NCT03720665&term=&cntry=&state=&city=&dist= 2) NCT04011670 https://clinicaltrials.gov/ct2/results?cond=&term=NCT04011670&cntry=&state=&city=&dist=.

Effects of caffeine ingestion on dynamic visual acuity: a placebo-controlled, double-blind, balanced-crossover study in low caffeine consumers

BACKGROUND

Acute caffeine ingestion has been associated with improvements in cognitive performance and visual functioning. The main objective of this study was to determine the effects of caffeine intake on dynamic visual acuity (DVA).

METHODS

Twenty-one low caffeine consumers (22.5 ± 1.6 years) took part in this placebo-controlled, double-blind, and balanced crossover study. In two different days and following a random order, participants ingested either caffeine (4 mg/kg) or placebo, and DVA was measured after 60 min of ingesting the corresponding capsule. A recently developed and validated software (moV& test, V&mp Vision Suite, Waterloo, Canada) was used to assess DVA.

RESULTS

We found a greater accuracy for both the horizontal and random motion paths of DVA after caffeine ingestion (p < 0.001 and p = 0.002, respectively). In regard to the speed of the response, our data revealed that caffeine intake was associated with a faster reaction time for horizontally (p = 0.012) but not for randomly (p = 0.846) moving targets. Also, participants reported higher levels of perceived activation after consuming caffeine in comparison to placebo (p < 0.001).

CONCLUSIONS

Our data suggest that caffeine intake (i.e., a capsule containing 4 mg/kg) has an ergogenic effect on DVA, which may be of special relevance in real-word contexts that require to accurately and rapidly detect moving targets (e.g., sports, driving, or piloting).

StimuliApp: Psychophysical tests on mobile devices

Psychophysical tests are commonly carried out using software applications running on desktop or laptop computers, but running the software on mobile handheld devices such as smartphones or tablets could have advantages in some situations. Here, we present StimuliApp, an open-source application in which the user can create psychophysical tests on the iPad and the iPhone by means of a system of menus. A wide number of templates for creating stimuli are available including patches, gradients, gratings, checkerboards, random-dots, texts, tones or auditory noise. Images, videos and audios stored in files could also be presented. The application was developed natively for iPadOS and iOS using the low-level interface Metal for accessing the graphics processing unit, which results in high timing performance.