topographical variability of erp response in older adults ... · • blinks corrected with matlab...

Electrophysiological Recordings • Recorded using a 256-Channel EGI System at 500 Hz with a vertex reference and impedances < 50 kΩ • Data were filtered offline at 1 to 30 Hz • Converted to an average reference • Blinks corrected with MATLAB regression module Results Behavioural Results Conflict Effect Conflict Effect Age Effect Age Effect C x A C x A Younger Adults show sensitivity to conflict p = .02 Older Adults fail to show sensitivity to conflict p = .76 Topographical Variability of N450 Response The site of maximal N450 activity (for each participant) was measured from AFz using a standard 256-channel EGI spherical coordinates map resulting in mean square deviation (MSD) scores [sqrt(x 2 + y 2 + z 2 )]. The MSD scores constitute the variability estimate in a 2 (groups) x 4 (conditions) ANOVA (see below). Summary As the level of interference increased, the variability of the N450 topography decreased in both groups. Therefore, older adults showed evidence of increased neural specificity that may mark more efficient information processing under greater task interference, a finding not anticipated on the basis of the compensation or dedifferentiation hypotheses. Analysis of topographical ERP response variability represents a novel means of identifying individual differences in PFC function and may constrain hypotheses based on age differences in the ERP components themselves. m Example Individual N450 Topographies: RC Condition Background Prefrontal cortex activity tends to be less selective in older adults (HAROLD Model) possibly the result of dedifferentiation of neural response or the addition of cognitive resources (compensation hypothesis) 1 . We hypothesized that, as the demands on executive control in working memory increased, older adults would show reduced selectivity of neural responses at recording sites over PFC (i.e., greater variability of N450 response 2 ). Method Participants 16 Young Adults 18 Older Adults 10 Female 12 Female Mean Age 20 (sd 1.9) Mean Age 74 (sd 7.9) Sternberg Design 3 Stimuli: b, c, d, f, g, h, j, k, l, m, n, p, q, r, s, t, v, w, x, z Duration: 45 minutes to complete 360 trials with 2000 ITI Presented in 6 randomized blocks Topographical Variability of ERP Response in Older Adults is Inversely Related to Interference in a Working Memory Task William J. Tays, Sidney J. Segalowitz, Karen Mathewson, & Jane Dywan Brock University, Canada References 1 Cabeza, R., Anderson, N.D., Lacontore,J.K., & McIntosh, A.R. (2002). Aging gracefully: compensatory brain activity in high- performing older adults. Neuroimage, 17, 1394-1402. 2 West, R. J. (2004). The Effects of Aging on Controlled Attention and Conflict Processing in the Stroop Task. Journal of Cognitive Neuroscience, 16, 103-113. 3 Nelson, K., Reuter-Lorenz, P. A., Sylvester, C.Y. C., Jonides, J. & Smith, E. (2003). Dissociable Neural Mechanisms Underlying Response-Based and Familiarity-Based Conflict in Working Memory. PNAS, 100, 11171-11175. Presented at Cognitive Neuroscience Society, New York, May 5-8, 2007. Supported by NSERC research grants to JD and SJS, and a student fellowship to KM. For more information, write to SJS at [email protected] p < .001 p < .001 p = .31 p < .001 p = .052 p = .47 50 60 70 80 90 100 110 Variance Estimate Negative Familiar High Familiar Response Conflict Condition Young Old Younger Adults Older Adults Conflict Effect: p < .01 Age Effect p < .05 Age x Conflict p = .25 ERP Results

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Page 1: Topographical Variability of ERP Response in Older Adults ... · • Blinks corrected with MATLAB regression module Results Behavioural Results Conflict Effect Conflict Effect Age

Electrophysiological Recordings

• Recorded using a 256-Channel EGI System at 500 Hz with avertex reference and impedances < 50 kΩ

• Data were filtered offline at 1 to 30 Hz• Converted to an average reference• Blinks corrected with MATLAB regression module

ResultsBehavioural Results

Conflict Effect Conflict EffectAge Effect Age Effect C x A C x A

Younger Adults showsensitivity to conflictp = .02

Older Adults fail to showsensitivity to conflictp = .76

Topographical Variability of N450 Response

The site of maximal N450 activity (for each participant) was measured from AFz using a standard 256-channel EGI spherical coordinates map resulting in mean square deviation (MSD) scores [sqrt(x2 + y2 + z2)]. The MSD scores constitute the variability estimate in a 2 (groups) x 4 (conditions) ANOVA (see below).

SummaryAs the level of interference increased, the variability of the N450 topography decreased in both groups. Therefore, older adults showed evidence of increased neural specificity that may mark moreefficient information processing under greater task interference, a finding not anticipated on the basis of the compensation or dedifferentiation hypotheses. Analysis of topographical ERP response variability represents a novel means of identifying individual differences in PFC function and may constrain hypotheses based on age differences in the ERP components themselves.

Example Individual N450 Topographies: RC Condition

Background

Prefrontal cortex activity tends to be less selective in older adults (HAROLD Model) possibly the result of dedifferentiation of neural response or the addition of cognitive resources (compensation hypothesis)1. We hypothesized that, as the demands on executive control in working memory increased, older adults would show reduced selectivity of neural responses at recording sites over PFC (i.e., greater variability of N450 response2).

MethodParticipants

16 Young Adults 18 Older Adults10 Female 12 Female

Mean Age 20 (sd 1.9) Mean Age 74 (sd 7.9)

Sternberg Design3

Stimuli: b, c, d, f, g, h, j, k, l, m, n, p, q, r, s, t, v, w, x, z

Duration: 45 minutes to complete360 trials with 2000 ITIPresented in 6 randomized blocks

Topographical Variability of ERP Response in Older Adults is Inversely Related to Interference in a Working Memory Task

William J. Tays, Sidney J. Segalowitz, Karen Mathewson, & Jane DywanBrock University, Canada

References1 Cabeza, R., Anderson, N.D., Lacontore,J.K., & McIntosh, A.R. (2002). Aging gracefully: compensatory brain activity in high-

performing older adults. Neuroimage, 17, 1394-1402. 2 West, R. J. (2004). The Effects of Aging on Controlled Attention and Conflict Processing in the Stroop Task. Journal of

Cognitive Neuroscience, 16, 103-113.3 Nelson, K., Reuter-Lorenz, P. A., Sylvester, C.Y. C., Jonides, J. & Smith, E. (2003). Dissociable Neural Mechanisms

Underlying Response-Based and Familiarity-Based Conflict in Working Memory. PNAS, 100, 11171-11175.

Presented at Cognitive Neuroscience Society, New York, May 5-8, 2007. Supported by NSERC research grants to JD and SJS, and a student fellowship to KM.For more information, write to SJS at [email protected]

p < .001p < .001

p = .31

p < .001p = .052p = .47

100

110

Variance Estimate

Negative Familiar HighFamiliar

ResponseConflict

Condition

YoungOld

You

nger