Effects of Caffeine on EEG Theta/Beta Ratio and Cognitive Control
Condition: Caffeine
Study type: Interventional

Summary: 
      Cognitive control driven by the prefrontal cortex (PFC) of the brain is thought to be
      important for goal-directed control over stimulus-driven processes. EEG-measured spontaneous
      theta/beta ratio (TBR) may potentially be used as an electrophysiological marker for this
      PFC-mediated cognitive control. In the present study the investigators further examine TBR as
      an electrophysiological marker for cognitive control, by administering caffeine to forty
      healthy female participants. After a first training session, participants will visit the lab
      twice in separate weeks, during which they will orally consume one capsule containing 200mg
      of caffeine, and one capsule containing a placebo substance (double-blind and random order of
      administration). EEG will be measured before and after capsule consumption, and cognitive
      control tasks will be administered after capsule consumption. Generally, the investigators
      expect that caffeine will decrease TBR and thereby increase cognitive control. Additionally,
      the investigators expect that individual differences in baseline frontal (reflected by TBR)
      and central dopaminergic (reflected by spontaneously-measured eye-blink rates; EBR) activity
      will moderate the relationship between caffeine and cognitive control. Furthermore, the
      effects of caffeine on specifically hypervigilance for threatening distractors (taking into
      account a possible moderating role of trait anxiety) were examined as a separate research
      question.
    

Detailed description: 
      BACKGROUND AND RESEARCH AIMS

      Cognitive control is an essential part of cognitive functioning, allowing top-down,
      goal-driven control over stimulus-driven, automatic processes. The prefrontal cortex (PFC) of
      the brain likely plays an important role in many aspects of cognitive control, including
      goal-driven attention, working memory, and emotion regulation. Previous EEG studies examining
      cognitive control have identified a potential electrophysiological marker for PFC-mediated
      cognitive control. These studies have found that the ratio between EEG-measured theta and
      beta brain oscillations is elevated in children with ADHD (who generally experience poor
      cognitive control), and in unselected adults with poor attentional control. This theta/beta
      ratio (TBR) is thought to reflect the extent to which prefrontal brain activity exhibits
      regulatory control over more posterior and subcortical brain areas, which has made this
      measure useful in the diagnosis and treatment of disorders related to poor cognitive control
      such as ADHD.

      In the present study, the investigators propose a new method to further validate TBR as an
      electrophysiological marker for cognitive control, by administering caffeine to participants.
      Caffeine is widely-known to improve various aspects of cognitive control, which would be
      expected to go alongside a decrease in TBR.

      Importantly, cognitive control benefits from both the maintenance of task-relevant
      representations and the flexible updating of these representations. These cognitive control
      functions may rely on somewhat different areas of the brain. Namely, whereas maintenance of
      task-relevant representations may be more dependent on PFC functioning, the flexible updating
      of these representations may rely more on dopaminergic activity in the striatum. Theta/beta
      ratio as a marker of PFC activity may thus specifically reflect task-relevant maintenance of
      information, and contrasting this EEG measure to a measure of striatal dopamine activity may
      shed more light on the nature of TBR. In the present study, the investigators will do so by
      measuring spontaneous eye-blink rates (EBR), which have shown to be sensitive to dopaminergic
      striatal activity.

      The first aim of the present study will be to further validate theta/beta ratio (TBR) as an
      electrophysiological marker for PFC-mediated cognitive control by administering caffeine to
      healthy participants. The investigators expect that (1a) theta/beta ratio will be inversely
      related to cognitive control performance (attentional focus, attentional shift, working
      memory; measured with TACT and N-back; possibly mainly related to TACT focus performance),
      (1b) caffeine will increase cognitive control performance, (1c) caffeine will decrease
      theta/beta ratio, and that (1d) these beneficial effects of caffeine on cognitive performance
      will be mediated by this decrease in theta/beta ratio.

      The second aim of this study will be to examine whether TBR and EBR differentially moderate
      the effects of caffeine on cognitive control. Namely, as these measures likely reflect
      activity of different brain areas, they may predict differential (possibly inverted U-shaped)
      effects of caffeine depending on their baseline activity. For example, increasing striatal
      dopamine through caffeine consumption may only be beneficial when initial striatal
      dopaminergic activity (as reflected by baseline EBR) is not too high in the first place,
      because when it is, this may then result in an increase in distractibility, rather than
      improved cognitive flexibility. As such, the investigators expect that (2a) baseline TBR will
      moderate the effects of caffeine on cognitive control performance (possibly mainly TACT focus
      performance), and that (2b) baseline EBR will moderate the effects of caffeine on cognitive
      control functioning (possibly mainly TACT shifting performance).

      The third aim of the present study will be to examine the effects of caffeine on emotional
      processing, and the role of TBR herein. Importantly, caffeine has traditionally been thought
      to increase threat-related processing and anxiety, especially in higher doses. However, an
      increasing number of animal studies are showing that small doses of caffeine may actually be
      anxiolytic. In part, this may be due to an increase in cognitive and attentional control
      capabilities. Namely, although the relation is complex, anxiety and attentional control
      influence each other mutually. Anxiety may increase vigilance for threat-related processing,
      whereas attentional control capabilities may protect against this. An optimal dose of
      caffeine could theoretically increase attentional control to the extent that this reduces
      over-processing of threat-related information. However, the dose-dependent effects of
      dopamine, nor-adrenaline, and caffeine predict that this optimal dosage depends on basal
      levels of these transmitters and therefore possibly on anxiety which is associated with
      increased dopamine and nor-adrenaline activity. The potential usefulness of moderate dosages
      of caffeine as a prophylactic drug for (attentional symptoms of) anxiety then may depend
      critically on such a possible moderating influence of anxiety. In the present study, the
      investigators examined this relation by taking into account the moderating effects of trait
      anxiety in the effects of caffeine on emotional processing. The investigators expect that
      (3a) higher TBR will be related to increased interference on the EST, (3b) a moderate dose of
      caffeine will decrease emotional interference on the EST, (3c) the effects of caffeine on
      emotional interference will be mediated by a change in TBR, and that (3d) the effects of
      caffeine on emotional interference will be moderated by individual differences in trait
      anxiety.

      Trait anxiety will be measured via self-report using the STAI-t, which will be added as a
      covariate in the analyses in which the relation between TBR and AC is examined. Finally, in
      this study the investigators will explore several other possible confounding factors in the
      relationship between caffeine consumption and cognitive control, including self-report
      measures of trait and state attentional control, anxiety, sleepiness, and ADHD symptoms.

      STUDY DESIGN

      A double-blind, randomized, placebo-controlled, cross-over trial. After a first training
      session, participants will visit the lab twice, separated by approximately one week. In these
      two lab sessions, participants will orally consume one capsule containing 200mg of pure
      caffeine (a similar amount of caffeine is found in about 2 cups of coffee) and one capsule
      containing a placebo filler substance (randomized and double-blind administration). Blinding
      and randomization of capsule allocation will be done by the pharmacy of the Leiden University
      Medical Center (LUMC).

      PARTICIPANTS

      Forty healthy female volunteers (aged 18-26 years) will participate in this study.
      Participants will be fairly naïve to caffeine consumption (drinking ≤100mg of caffeine, or
      about one cup of coffee, per day), and will be asked to abstain from caffeine and alcohol
      consumption for 12h before the start of the lab sessions. Participants will be students
      recruited at Leiden University through various advertisements (e.g., at the university
      campus). Participants who have withdrawn from the study will, when possible, be replaced by
      another randomly selected participant. For such replacement participants, the LUMC pharmacist
      has prepared blinded capsules containing placebo and caffeine in the same order as the
      original participant that they are replacing.

      PROCEDURES

      After online screening procedures, eligible participants will be tested at the same time on
      three separate days. Test sessions will take place between 10:00 and 17:00, lasting
      approximately 2 hours per session. Participants will be asked to abstain from alcohol and
      caffeine consumption for 12 hours before the start of the experiment. On the first testing
      (training) day, participants will complete questionnaires assessing demographics, trait
      levels of attentional control (ACS), trait anxiety levels (STAI trait subscale), habitual
      sleepiness (ESS), and ADHD symptoms (ADHD Rating Scale-IV). Furthermore, resting-state EEG (8
      minutes in alternating 1-minute blocks of eyes open/closed) and spontaneous EBR (one
      eyes-open block of 4 minutes) will be measured. In addition, participants will be
      familiarized with the cognitive tasks (TACT; N-Back; EST). Participants will complete these
      measures to reduce novelty or learning effects in subsequent test sessions. On each day of
      testing, state questionnaires (current sleepiness, KSS; attentional control, VAS; and
      anxiety, STAI state subscale) will be administered between each 4min (EBR) and 8min (EEG)
      baseline measure, and at the end of the day (i.e., administered twice on the first training
      day, and three times on the day 2/3 consumption days).

      The second testing day will be approximately one week after the first testing day. Prior to
      capsule consumption, EEG and EBR will be measured. Participants will then receive a capsule
      containing either caffeine (200mg) or placebo (double-blind, randomized administration).
      After a 30 minute break (as caffeine takes about half an hour to become active), EBR and EEG
      will be measured again. Finally, participants will complete the same cognitive tasks they
      completed on the first day.

      On the third testing day the testing protocol of the second day will be repeated, with the
      exception that the other, remaining caffeine (200mg) or placebo capsule will be administered.

      COGNITIVE CONTROL TASKS

      All cognitive tasks (TACT; N-Back; Emotional Stroop Task) are programmed and completed on a
      computer using E-Prime (v2.0). The cognitive control tasks are described below.

        1. Two-Factor Attentional Control Task (TACT): The TACT is a global/local congruency task
           which aims to measure attentional focusing and attentional shifting. In this task,
           participants are shown a large arrow that consists of several smaller arrows pointing in
           the same (congruent) or opposite (incongruent) direction. Participants are instructed to
           respond to the direction of the large arrow or smaller arrows as fast as possible
           without making too many mistakes. They can do so by pressing the left or right arrow key
           on a keyboard, using the index and middle fingers of their dominant hand. Prior to the
           appearance of an arrow, participants see a grey screen for 500ms after which the word
           "Large" in the colour blue or "Small" in the colour yellow appears for 500ms, which
           indicates which arrow participants have to respond to. After a 250ms grey screen the
           arrow appears in the middle of the screen, which disappears after 2000ms or when a
           response is given. On each trial, the arrow appears in a slightly different position to
           ensure that participants look at the arrow rather than fixate on a few pixels on the
           screen (which in theory could be sufficient to identify the direction of the arrows).

           In the attentional focus part of the task, participants complete two blocks of 52 trials
           each. In one block participants only respond to the direction of the large arrow, and in
           the other block participants only respond to the direction of the smaller arrows. TACT
           focus performance is measured by subtracting RTs on congruent trials (i.e., trials in
           which no inhibition of distraction of non-attended arrows is necessary) from RTs on
           incongruent trials (i.e., trials in which participants have to inhibit their response to
           the distraction of non-attended arrows). As such, smaller differences in RTs indicate
           better focus performance. In the attentional shift part of the task, participants
           complete two blocks of 120 trials, separated by a one-minute break, in which the
           direction of the arrow to which participants have to respond changes every six trials
           (i.e., 40 shifts in total). TACT shift performance is calculated by subtracting RTs on
           the last two trials before an attentional shift from RTs on the first two trials after
           an attentional shift (i.e., trials in which participants shifted their attention from
           looking at larger to smaller arrows or vice versa). As such, smaller differences in RTs
           indicate better shifting performance. The two trials before and after a shift are always
           incongruent to increase the difficulty (and thus likely the shift costs) of this task.
           The order of focus blocks (i.e., large arrow or smaller arrows first), and the order of
           first completing focus or shift blocks, are counterbalanced over participants. Trials in
           which participants give incorrect responses, or improbably slow or fast responses, are
           not further analysed.

        2. N-Back Task: The N-back task is a task that assesses different working memory processes.
           In the N-Back task, participants are sequentially shown letters. Participants have to
           indicate whether the current letter matches the letter shown n places before, using the
           1 ("same letter") or 2 ("different letter") on a keyboard. The 1-back and 3-back tasks
           were administered, as caffeine likely has the biggest influence on 3-back task
           performance, and may not greatly differentially influence 1-back and 2-back task
           performance. For each n-back condition, 75 letters are shown in total, of which 25 (33%)
           are hits (i.e., trials which were shown n places back). The first three trials of each
           block are never targets. Each letter is shown for 500ms, which is followed by a 1500ms
           blank screen. Participants can respond to the letter in this entire 2000ms interval.
           Prior to each n-back condition, participants receive instructions and examples of the
           task (under supervision of the researcher on the training day), and complete 21 training
           trials (7 hit trials), to make sure that they understand the task. The order of 1-back
           and 3-back completion will be counterbalanced over participants. Performance is measured
           by examining accuracy scores (% correct), and by examining RTs on correctly-answered
           trials.

        3. Emotional Stroop Task (EST): The EST is a variant on the traditional Stroop task (in
           which participants have to name the colour of a word printed in a different colour name,
           e.g. name the colour of the word "Red" written in blue ink). In the EST,
           emotionally-laden pictures are shown, on which a coloured square is superimposed.
           Participants have to respond to the colour of the square, and as such have to inhibit
           the distracting influence of the pictures. Pictures are chosen from the IAPS database
           and are selected based on their balance and arousal ratings to represent three picture
           conditions: neutral, negative, and positive. For each of the picture condition, 4
           pictures (each time with the square in a different location: top or bottom x left or
           right) are shown 8 times (i.e., 32 trials per condition, 96 trials in total). The colour
           of the square is randomly chosen from three possible options (red, yellow, or blue) on
           each trial. During each trial, first, a picture is shown for 200ms, after which a
           coloured square is superimposed on this picture in one of four possible locations.
           Participants then get 1800ms to respond to the colour of the square, which they can do
           using coloured buttons of a standard response box. Then, a 2000ms grey screen is shown,
           after which the next picture appears. Prior to the actual task, participant complete 24
           practice trials in which neutral pictures are shown. Performance on the Emotional Stroop
           Task is measured by examining RTs on the negative and positive condition trials,
           compared to RTs on neutral condition trials, on correctly-answered trials.

      QUESTIONNAIRES

      All trait questionnaires (ACS; STAI-t; ADHD Rating Scale-IV; ESS) are programmed and
      completed on a computer using E-Prime (v2.0). State questionnaires (STAI-s; VAS AC-s; KSS)
      are completed using pen and paper. The questionnaires are described below.

        1. Attentional Control Scale (ACS): A modified Dutch translation of the ACS will be
           administered to participants. The ACS aims to measure trait attentional control, as
           assessed with 20 statements measuring attentional shift (e.g., "I can quickly switch
           from one task to another"), attentional focus (e.g., "My concentration is good even if
           there is music in the room around me") and flexible thought (e.g., "I have a hard time
           coming up with new ideas quickly"). Participants have to indicate to what extent the
           statements reflect their attentional control on a 4-point scale, ranging from 1 ("almost
           never") to 4 ("always").

        2. State-Trait Anxiety Index (trait subscale; STAI-t): The trait scale of the Dutch STAI
           consists of 20 items measuring trait anxiety (e.g., "I worry too much over something
           that really doesn't matter"). Participants can respond to these items using a 4-point
           rating scale, ranging from 1 ("almost never") to 4 ("almost always").

        3. ADHD Rating Scale-IV: A modified Dutch translation of the ADHD Rating Scale-IV will be
           administered to participants. This questionnaire consists of 23 items measuring ADHD
           symptoms of hyperactivity/impulsivity (e.g., "I feel restless") and inattention (e.g.,
           "I am quickly distracted"). Participants are asked to rate the extent to which the item
           applied to them during the past 6 months, on a scale of 0 ("Never or rarely") to 3
           ("Very often").

        4. Epworth Sleepiness Scale (ESS): The ESS is used as a measure of habitual sleepiness. On
           the ESS, participants are asked to rate how likely it is that they would doze off in
           eight usual and recent situations (e.g., "While watching television"), using a scale of
           0 ("Would never doze off") to 3 ("High chance of dozing").

        5. State-Trait Anxiety Index (state subscale; STAI-s): The state scale of the Dutch STAI
           consists of 20 items measuring how anxious participants feel at this moment (e.g., "I
           feel calm", "I am worrying"). Participants can respond to these items using a 4-point
           rating scale, ranging from 1 ("Not at all") to 4 ("A lot").

        6. Karolinska Sleepiness Scale (KSS): The KSS is a 9-point VAS assessing subjective,
           instantaneous sleepiness. Participants are asked to report how alert or sleepy they are
           on a scale of 1 ("Very alert") to 9 ("Very sleepy (fighting sleep)").

        7. VAS AC-s: The VAS attentional control scale consists of six items assessing
           participants' current feelings of attentional control (e.g. "I have trouble
           concentrating"). Participants have to indicate to what extent the item reflects their
           current attentional control by marking 100mm lines, anchored with "Not at all" and "A
           lot" on the left and right sides.

      EBR AND EEG MEASUREMENT

        1. Spontaneous eye-blink rates (EBR): Spontaneous EBR will be collected in a 4 min.
           eyes-open block using vertical EOG, which records voltage differences between two
           electrodes placed above and below the eye. In this 4 min. interval, participants will be
           asked to look at a central point in the room in a relaxed state. Individual EBR will be
           calculated by dividing the total number of eye blinks during the 4 min. interval by 4.

        2. Spontaneous EEG: Spontaneous EEG will be recorded for 8 min. continuously in alternating
           1-min blocks of eyes open/eyes closed recording. EEG recordings will be acquired across
           the scalp using 16 electrodes, positioned according to international 10/20 system, using
           the ActiveTwo BioSemi system. Electrodes will be placed at the left and right mastoids
           for offline re-referencing of the scalp signals to the average of the mastoid signals.
           To measure eye and blink movements, electrooculogram (EOG) electrodes will be placed
           above and below the left eye (vertical EOG) and external canthi of each eye (horizontal
           EOG). Offline data processing will be done in Brain Vision Analyzer V2.02. A 0.1-Hz
           high-pass filter, 100-Hz low-pass filter, and 50-Hz notch filter will be applied. Data
           will be analyzed in four-second segments. The data will be automatically corrected for
           ocular artifacts and segments containing remaining artifacts will be removed. A fast
           Fourier transformation (with a resolution of 0.25 Hz, using a hamming window of 10%)
           will be applied to calculate area power density for the beta (13-30 Hz), and theta (4-7
           Hz) frequency bands. The power densities for the three frontal electrodes will be
           averaged into measures for frontal beta and frontal theta power density, and used to
           calculate theta/beta ratios, which will be log-transformed in case of non-normality.

      DATA PROCESSING

      Outlier removal for each cognitive task will be done on a trial-to-trial basis (excluding
      improbably fast and/or slow responses) for each participant. First a rough RT removal will be
      applied, after which a more sophisticated removal of outlying trials will be conducted. Based
      on previous studies with these tasks, the following trials will be removed:

        1. TACT: trials faster than 200ms or slower than 1200ms, after which trials completed
           faster or slower than 2.5 SDs of the mean RT for that task will be removed.

        2. N-Back: trials faster than 300ms will be removed.

        3. EST: trials faster than 300ms or slower than 1200ms, after which trials completed faster
           or slower than 2.5 SDs of the mean RT for that task will be removed.

      There is some evidence of the stability of TBR and EBR over time, which complies with the
      notion that these markers reflect stable, trait-like neural processes. However, the influence
      of state-dependent circumstances on these measures are still not fully understood. In the
      present study, baseline TBR and EBR will be measured on each day of testing, but only one of
      those TBR and one of those EBR baseline measures will be used as trait-like neural marker in
      the moderation analyses. The selection of which of these baseline measures will be used in
      the moderation analyses, is based on the following rules:

        1. If the investigators find that TBR or EBR baseline measures on day 1 are highly similar
           (mean comparison and/or correlation) to their corresponding baseline measures on day 2
           and day 3, the day 1 baseline measures will be used in the moderation analyses.

        2. If the investigators find that TBR or EBR baseline measures on day 1 differ greatly from
           their corresponding baseline measures on day 2 OR day 3, the day 1 baseline measures
           will be used in the moderation analyses.

        3. If the investigators find that TBR or EBR baseline measures on day 1, day 2, and day 3,
           all differ greatly from each other, the day 1 baseline measures will be used in the
           moderation analyses.

        4. If the investigators find that TBR or EBR baseline measures on day 2 and day 3 are
           highly similar, but differ greatly from their corresponding baseline measures on day 1,
           the averaged baseline measures of day 2 and day 3 will be used in the moderation
           analyses.
    

Intervention name(s): Caffeine (200mg); Placebo
Intervention type(s): Dietary Supplement; Other
Intervention description(s): Oral consumption of capsule containing 200mg caffeine.; Oral consumption of capsule containing a placebo substance.
Intervention MeSH terms: Caffeine
Allocation: Randomized
Intervention model: Crossover Assignment
Masking: Double (Participant, Investigator)
Primary purpose: Basic Science
Keywords: Caffeine; EEG; Theta/beta ratio; Eye-blink rates; Cognitive control; Emotional Stroop; Global/local congruency; N-Back; Prefrontal Cortex