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

Not Applicable

Completed

• Conditions: Cognitive Flexibility
• Interventions: Combination Product: Anodal tDCS and balanced drink; Combination Product: Anodal tDCS and tyrosine depleted drink; Combination Product: Sham tDCS and balanced drink; Combination Product: Sham tDCS and tyrosine depleted drink

• Registration Number: NCT03462303
• Lead Sponsor: Sheffield Hallam University

Brief Summary

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.

Detailed Description

Not available

Study Timeline

• Study Start: 2018-02-12
• Study First Submitted: 2018-02-20
• Study First Submitted QC: 2018-03-08
• Study First Posted: 2018-03-12
• Primary Completion: 2018-06-30
• Study Completion: 2018-06-30
• Status Verified: 2018-09
• Last Update Submitted: 2018-09-10
• Last Update Posted: 2018-09-11

Recruitment & Eligibility

• Status: COMPLETED
• Sex: All
• Target Recruitment: 36

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

Study & Design

• Study Type: INTERVENTIONAL
• Study Design: FACTORIAL

Arm && Interventions

Group	Intervention	Description
tDCS anodal + balanced drink	Anodal tDCS and balanced drink	-
tDCS anodal +tyrosine depleted drink	Anodal tDCS and tyrosine depleted drink	-
tDCS sham + balanced drink	Sham tDCS and balanced drink	-
tDCS sham + tyrosine depleted drink	Sham tDCS and tyrosine depleted drink	-

Primary Outcome Measures

Name	Time	Method
Change in cognitive flexibility performance	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

Trial Locations

Locations (1)

Department of Psychology labs; 🇬🇧 Sheffield, South Yorkshire, United Kingdom