Dissociation of motor and sensory inhibition processes in normal aging

Abstract

Objective: Age-related cognitive impairments have been attributed to deficits in inhibitory processes that mediate both motor restraint and sensory filtering. However, behavioral studies have failed to show an association between tasks that measure these distinct types of inhibition. In the present study, we hypothesized neural markers reflecting each type of inhibition may reveal a relationship across inhibitory domains in older adults.

Methods: Electroencephalography (EEG) and behavioral measures were used to explore whether there was an across-participant correlation between sensory suppression and motor inhibition. Sixteen healthy older adult participants (65-80 years) engaged in two separate experimental paradigms: a selective attention, delayed-recognition task and a stop-signal task.

Results: Findings revealed no significant relationship existed between neural markers of sensory suppression (P1 amplitude; N170 latency) and markers of motor inhibition (N2 and P3 amplitude and latency) in older adults.

Conclusions: These distinct inhibitory domains are differentially impacted in normal aging, as evidenced by previous behavioral work and the current neural findings. Thus a generalized inhibitory deficit may not be a common impairment in cognitive aging.

Significance: Given that some theories of cognitive aging suggest age-related failure of inhibitory mechanisms may span different modalities, the present findings contribute to an alternative view where age-related declines within each inhibitory modality are unrelated.

Figure 1

Schematic illustration of the selective attention, delayed-recognition task. In this task, participants were required to report with a button press whether the probe stimulus matched one of the previously presented stimuli (a face or scene stimulus). In the passive view response period, an arrow was presented, and participants were required to make a button press indicating the direction of the arrow. The lines below the stimuli are used to highlight task-relevance in this illustration and were not present in the actual task.

Figure 2

Schematic illustration of the stop signal task. The interval between horizontal (“GO” signal; 75% of trials) and vertical arrows (“STOP” signal; 25% of trials) in the stop trials becomes shorter/longer in steps of 50 ms depending on each participant's performance, ensuring 50% of correctly inhibited and 50% failed stop trials for each participant.

Figure 3

ERPs from the selective attention, delayed-recognition task at the electrode of interest where the effect was greatest across all conditions, P10 (grey circle). The solid black line indicates attended faces, dashed black line indicates ignored faces and the solid gray line represents the passive view condition. Both P1 amplitude and the N170 latency displayed a suppression deficit, while only N170 latency also showed an enhancement effect.

Figure 4

ERPs time-locked to STOP signal for successful inhibition (SI; bold line) and failed inhibition (FI; dotted line) stop trials averaged across all participants at the electrode of interest where the effect was greatest across all conditions, electrode FCz (grey circle). There was a significant difference between conditions for the latency, but not for amplitude, for each component (N2/P3).

Figure 5

Inter-task correlations. R-values for each inter-task correlation are presented, with the 95% confidence interval for each correlation presented in parentheses. The grey dashed line at -.497 and +.497 represent p< .05 level of significance.