Transcranial Direct Current Stimulation
Conditions
Brief summary
Cathodal Transcranial direct current stimulation (tDCS) was administered to the right parietal region in order to determine if this stimulation could disrupt awareness of the conditioned stimulus (CS) - unconditioned stimulus (US) relationship in a classical conditioning experiment.
Interventions
DEVICEtranscranial direct current stimulation
transcranial direct current stimulation applied at 2 mA over the right parietal region for 20 min
DEVICEsham transcranial direct current stimulation
transcranial direct current stimulation applied at 2 mA over the right parietal region for 30 sec
Sponsors
National Institute on Aging (NIA)
Johns Hopkins University
Study design
Allocation
RANDOMIZED
Intervention model
PARALLEL
Primary purpose
BASIC_SCIENCE
Masking
SINGLE (Subject)
Eligibility
Sex/Gender
ALL
Age
20 Years to 30 Years
Healthy volunteers
Yes
Inclusion criteria
* Educational attainment of at least eight years and English as the native language * Mini-Mental State Examination (MMSE) score of 26 * Normal episodic memory (i.e., CERAD word List Recall \> 5) * Informed consent; 5) age of 20-30
Exclusion criteria
* Disturbed consciousness * Other neurological or systemic disorder which can cause dementia or cognitive dysfunction * Prior history of a major psychiatric disorder * History of definite stroke * Focal lesion on MRI exam * Use of anxiolytic, antidepressant, neuroleptic, or sedative medication * Predominately left-handed * Has MRI contraindication such as pacemaker, implanted pumps, shrapnel, etc. (full MRI screening form will be filled out).
Design outcomes
Primary
| Measure | Time frame | Description |
|---|---|---|
| CS-US Awareness | recorded immediately after the 20 minutes of tDCS stimulation | To assess CS-US awareness, we used a questionnaire The questionnaire consists of 7 true/false questions about the sequence and co-occurrence of the conditioned stimulus (CS, a 1000 Hz tone) and unconditioned stimulus (US, a 100 ms puff of air to the eye). The score can thus range from 0 to 7. Higher score values indicate better awareness of the sequence and co-occurrence of the CS and US |
Secondary
| Measure | Time frame | Description |
|---|---|---|
| Line bisection test of left-hemifield neglect | recorded immediately after primary awareness questionnaire | The subject is given a sheet of paper with a number of horizontal lines on it. The subject is instructed to cut each line in half by drawing a small pencil mark through each line. The test is scored by measuring the percent deviation, which is calculated by the following formula: Percent deviation=100 x (measured left half - true half)/true half This yields positive numbers for marks placed to the right of center, and negative numbers for marks placed to the left of center. Patients with right hemisphere damage and contralateral neglect show higher positive line bisection scores compared to healthy controls or patients without right hemisphere damage and vice versa. |
| Eyeblink conditioned responding | recorded during the tDCS administration | Eyeblink conditioning is recorded while the subject watches a silent movie. For conditioning, the conditioned stimulus (CS) is a 1350 ms 1000 Hz tone. This tone co-terminates with a 100 ms left corneal airpuff (5 psi). 30 CS-US presentations are delivered at an average rate of one every 18 sec. Conditioned responses (CRs) are defined as follows: the difference between the maximum and minimum responses in a 500 ms pre-US time window must exceed four times the standard deviation of the mean of the baseline period (250 ms pre-CS presentation). The 500 ms pre-US time window was selected to minimize the inclusion of voluntary and alpha responses as CRs. Performance is expressed as % CRs, that is, the percent of trials in which a CR occurred. Greater numbers indicate greater amounts of learning. |
Outcome results
None listed