Perceptual deterioration is reflected in the neural response: fMRI study of nappers and non-nappers

Abstract

Repeated training on a perceptual task can result in performance deterioration. In the case of vision, this practice-dependent decrease, or perceptual deterioration is restored by changing the target orientation, spatial location, or by taking a daytime nap. Behavioral studies suggest the locus of these performance changes to be primary visual cortex. We used fMRI to directly probe whether perceptual deterioration and nap-dependent maintenance of performance can be detected at the level of primary visual cortex. We also asked whether these changes are due to a bottom-up, stimulus-driven response or a top-down plasticity of attentional mechanisms. Subjects were scanned while performing a texture-discrimination task. Half the subjects took a nap between sessions. We measured the relationship between changes in performance and changes in BOLD signal modulation between the two groups. Non-nappers showed performance deterioration that was significantly correlated with decreased BOLD signal modulation, exclusively in area V1 and limited to the bottom-up condition. In contrast, no change was detected in performance and BOLD response in the two conditions for nappers. These results indicate that napping prevented performance deterioration, which was reflected in the fMRI response of neurons in V1. Without a nap, perceptual deterioration was related to decreases in the stimulus-driven, bottom-up representation, rather than decreases in attentional modulation to the stimulus.

Figure 1

Testing schedule for nap and no-nap groups

Figure 2

fMRI conditions: Scans were structured in a blocked design in which half of the trials directed the subject to perform the task with the target on the trained side and half on the untrained side. The Attention Only condition (2A & 2B) measured top-down modulation to a region of interest where there was an attended stimulus (indicated by circle) versus an unattended region with a stimulus (indicated by square). The Stimulus + Attention condition (2C. & 2D) measured bottom-up modulation to a region of interest where there was an attended stimulus (indicated by circle) versus an unattended region with no stimulus (indicated by square).

Figure 3

Texture discrimination difference threshold in nappers and non-nappers.

Figure 4

Plot of difference scores for TDT and BOLD signal of the Stimulus+Attention condition on the trained side of V1 in nappers and non-nappers. In non-nappers, a linear relationship was found between decreases in task performance and decreases in BOLD signal.

Figure 5

Plot of difference scores for TDT and BOLD signal of the Attention Only condition on the trained side of V1 in nappers and non-nappers. No relationship was found between changes in task performance and BOLD signal modulation.