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OpenTrials
Completed

NCT Number: NCT03462303

Modulation of Cognitive Flexibility by Tyrosine Depletion and Transcranial Direct Current Stimulation

The dorsolateral prefrontal cortex (dlPFC) and dopamine (DA) have been implicated in the control of cognitive flexibility. However, while a great deal of what it is know regarding a causative relationship between cognitive flexibility and its neuronal underpinning comes from animal studies, human data have largely been correlational (i.e. imaging investigations). In a recent study, the current research group examined whether putative increases in dopamine levels through tyrosine administration and blockage of these by cathodal (i.e. inhibitory) transcranial direct current stimulation (tDCS) of the dlPFC could be causally related to cognitive flexibility as measured by task switching and reversal learning.

The next step involves finding a way of lowering dopamine concentrations while anodal (i.e. excitatory) stimulation of the dlPFC is applied and cognitive flexibility measured. One experimental approach to reduce global DA synthesis and transmission is through acute phenylalanine and tyrosine depletion (APTD). This dietary intervention involves the administration of an amino-acid mixture lacking in tyrosine and phenylalanine, which can be used to selectively lower DA synthesis in humans.

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Key information

Conditions

Cognitive Flexibility

Age range

18 year–30 year

Sex eligibility

All sexes

Study type

Interventional

Phase

Not applicable

Primary location

Department of Psychology labs

Sheffield, South Yorkshire, S10 2BQ, United Kingdom

Who can participate

Healthy volunteers accepted: Yes

Only the study team can determine whether someone qualifies for participation.

Inclusion criteria

  • Either male or female
  • You are aged between 18 and 30 years
  • You are in good health
  • You agree to fast overnight prior to testing

Exclusion criteria

  • Are suffering from cardiac, hepatic, renal, or neurological disorders
  • Damaged or diseased skin on your face and scalp, or a sensitive scalp
  • A history of alcohol or drug addiction, or severe psychiatric illness
  • Are in drug treatment which may lower seizure threshold (i.e. epilepsy)
  • You are pregnant
  • Slept less than 6 hours prior to coming to the lab
  • Suffer from phenylketonuria
  • A history of or current experience of migraine or headaches
  • A history of or current use of antidepressants
  • A history of or current use of tyrosine supplements
  • Consume more than five beverages containing caffeine per day

Treatment and study plan

Sham tDCS and tyrosine depleted drink

Combination Product

Transcranial direct current stimulation (sham) of the dlPFC in combination with a tyrosine and phenylalanine free product.

Anodal tDCS and tyrosine depleted drink

Combination Product

Transcranial direct current stimulation (anodal) of the dlPFC in combination with a tyrosine and phenylalanine free product.

Sham tDCS and balanced drink

Combination Product

Transcranial direct current stimulation (sham) of the dlPFC in combination with a drink containing both tyrosine and phenylalanine.

Anodal tDCS and balanced drink

Combination Product

Transcranial direct current stimulation (anodal) of the dlPFC in combination with a drink containing both tyrosine and phenylalanine.

Primary outcomes

  1. Change in cognitive flexibility performance

    Time frame: Measured over 5 hours four times.1st measurement taken at baseline (i.e. time 0). 2nd measurement taken 120 minutes after measurement 1. 3rd measurement taken 220 minutes after measurement 1. 4th measurement taken 270 minutes after measurement 1.

    Measured using Wisconsin Card Sorting Test

  2. Change in cognitive flexibility performance

    Time frame: Measured over 5 hours. 1st measurement taken at baseline (i.e. time 0). 2nd measurement taken 120 minutes after measurement 1. 3rd measurement taken 220 minutes after measurement 1. 4th measurement taken 270 minutes after measurement 1.

    Measured using Probabilistic Reversal Learning

Sponsors and collaborators

Lead sponsor

Sheffield Hallam University

Other

Registry information

Important dates

Study start
2018
Primary completion
2018
Study completion
2018
First posted
Mar 12, 2018
Registry last updated
Sep 11, 2018

OpenTrials presents study information sourced from ClinicalTrials.gov. The official registry record should be consulted for the latest information.

View the official ClinicalTrials.gov record (opens in a new tab)

This listing is for discovery and informational purposes only. It is not medical advice, does not guarantee that a study is recruiting, and does not determine eligibility. Contact the study team and a qualified healthcare professional when considering participation.

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