Cognitive Aging and Inhibitory Functions: an Investigation on Functional Neural Activities and Neurotransmitters(1/3)

Inhibitory functions are crucial for keeping our behaviors under control, and it is prone to the influence of aging. In the current project, we are going to investigate how the following aspects of inhibitory functions are modulated by aging: 1) controlled vs. automatic inhibition; 2) the temporal evolution of controlled vs. automatic inhibition; 3) response- vs. object-based automatic inhibition. A set of six experiments are proposed to investigate effects of aging on the functional and neuronal mechanisms of the inhibitory processes with behavioral (Experiment 1, 3, and 5) and activation/neurotransmission (FMRI/MRS: Experiment 2 and 6; ERP/MRS: Experiment 4) measurements in a project spanning across four years. In Experiment 1, we aim to demonstrate the dissociation between explicit and implicit inhibitory processing across the young, middle-age, and elderly groups by a Stroop NP paradigm, which would consist of NP and non-NP Stroop conditions. Results of Experiment 1 will help to optimize the experimental settings for the subsequent Experiment 2 using FMRI and MRS to identify the neural networks and the associated GABA concentration related to the explicit and the implicit inhibitory processes for each age group. We will then move on to further examine aging-related changes in the inhibitory control processes by testing the inhibitory rebound effects. In Experiment 3, we will manipulate the inter-trial interval (ITI) in Stroop NP paradigm to modulate the processing of the inhibitory rebound on the distractor. The temporal dissociation of the inhibitory rebound effects among age groups will be further investigated with the ERP method in Experiment 4, targeting the N2 component associated with the inhibitory processing. The relationship between GABA modulation and N2 characteristics (latency/amplitude) will also be examined. After studying the dissociation between controlled and automatic inhibition as well as their respective time course in the three age groups, we will then go on to examine changes of object- and response-based representations across age. Specifically, Experiment 5 will instruct the participant to employ two different internal representations, namely the object-and response-based strategies, in a NP task to study how each strategy changes with aging, and then in Experiment 6 we will apply FMRI and MRS to study how the functional characteristics of inhibitory neural networks and GABA concentration are differentially related across the three age groups. To summarize, the current project will advance our understanding of the impact of aging on the behavioral and neural characteristics of inhibitory processes, and shed light on various topics that have not been thoroughly investigated in the literature on inhibition.