fMRI Analysis of Aging and Awareness in Conditioning

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

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 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.