P3 target cue target long CTI cue target cue short CTI children old PZ cue target Cue-related ERPs P3 cue cue young PZ target MIXING COSTS RELIABLE SWITCH COSTS ERP evidence for life-span development of executive functions: the roles of task preparation and interference control in a cued task-switching paradigm Daniela Czernochowski 1, Yael M. Cycowicz 2, Marianne de Chastelaine 1, Cort Horton 1 and David Friedman 1 1 Cognitive Electrophysiology Laboratory, and 2 Division of Brain Stimulation, NY Psychiatric Institute, NY, NY The ability to prepare for a task switch showed a clear lifespan progression (Fig. 6), suggesting that only young adults prepared efficiently. Both older adults and children benefited from additional preparation - older adults were able to improve their speed (Fig 5), while children improved their accuracy (Fig 2). Following efficient preparation, young adults were able to exert the cognitive control necessary to respond accurately and quickly even to incongruent switches (Figs. 2-5). Hence, Fig 7 suggests only small amounts of response conflict for the young, as indexed by MFN amplitude [5]. As a result of inefficient preparation, response conflict appeared heightened in all incongruent conditions in older adults and children (Fig 7), and in large RT interference costs (Fig 5). Hence, conflict monitoring and detection appear intact in older adults [5] and children. However, whereas children committed many errors, older adults’ performance was slow, but very accurate (Fig 2). A frontal negative-going activity (largest at frontal sites) ~250ms prior to the response was evident for incongruent switch trials only in older adults (Fig 7). This recruitment of additional, putatively frontal, resources to counteract the heightened response conflict following inefficient preparation, could have enabled older adults to perform very accurately at the expense of prolonged RTs, consistent with the recently-proposed “load- shift-model” [6]. Children do not appear to recruit these additional control processes following incomplete preparation (Fig 6). That is, unlike older adults, despite their long RTs, they showed much lower accuracy, perhaps due to incomplete frontal lobe maturation [7]. Participants: Children (n= 10, mean = 10.4 years, range 9-11) Young adults (n= 20, mean = 23.3 years, range 20-27) Older adults (n= 20, mean = 73.5 years, range 61-83) EEG Methods: 62 sintered Ag/AgCl electrodes, ref: averaged mastoids; Continuous DC- 100 Hz, 500 Hz sampling rate Design: Short and long (600 vs ms) CTIs Two tasks: How Many ? What Number ? 4 stimulus displays (1, 111, 3, 333) in homogeneous and mixed- task blocks [3] Congruent trials: 1 and 333 require the same response Incongruent trials: 111 and 3 require different responses Methods Summary and DiscussionResultsIntroduction Task switching requires executive processes, such as preparing a currently-relevant task set while inhibiting the previous one. Incongruent stimulus-response mappings cause response conflict, leading to reduced accuracy and longer RTs in mixed-task blocks [1], which can be reduced by advance preparation [2]. Relative to young adults, difficulties in these processes are observed in children and older adults [3, 4]. However, it is currently unclear which of these control processes is still maturing in children or compromised in older adults. ERPs were recorded to assess lifespan differences, which were predicted to occur during the cue-target interval (CTI), reflecting inefficient preparation. As a result, we expected increases in medial frontal negativity (MFN), a response-locked index of response conflict [5], in children and older adults. We predicted that additional preparation time prior to a switch might ameliorate these hypothesized lifespan differences. References 1 Mayr (2001). Psychol Aging 16, Monsell (2003). Trends Cogn Sci 7, Cepeda et al. (2000). J Abnorm Child Psychol 28, Kray & Lindenberger (2000). Psychol Aging 15, Nessler et al. (2006). Neurobiology of Aging 6 Velanova et al. (2007). Cer Cortex 17, Bunge et al. (2002). Neuron 33, Mixing costs – RT differences between non-switch trials in mixed vs. homogeneous blocks – were larger for children and older relative to younger adults (Fig 3). Switch costs - RT differences between switch and non-switch trials within mixed blocks - were generally much smaller than mixing costs (Fig. 4 vs. Fig 3). Children had larger switch costs than both adult groups. For the latter groups, switch costs were only reliable for incongruent trials after both CTIs in older adults and after the short CTI in young adults. Incongruent relative to congruent trials were associated with longer RTs (Fig 3). These interference costs were larger for children and older relative to younger adults. With additional time to prepare, RT Interference costs were reduced in older adults (Fig 5), while children committed fewer errors to incongruent switch trials (Fig 2). ERPs to the cue (Fig 6) suggest group differences in preparation for a switch. While all groups show larger P3 amplitudes in mixed than homogenous blocks, the distinction between switch and non- switch trials is delayed for children (suggesting incomplete preparation) and reduced in amplitude for older adults (suggesting inefficient preparation). …response CTI=600 vs ms congruent trial incongruent trial short: 300 ms long: 900 ms 300 ms 1 What Number? + SWITCH Response-Cue Interval 1000 ms 111 How Many ? + + …response Response-locked ERPs– short CTI Children committed more errors than young adults, who in turn made more errors than older adults. * PERCENT ERROR IN INCONGRUENT TRIALS INTERFERENCE COSTS RT incongruent – RT congruent FCZ non-switch homogeneous switch 5 µV + - MFN amplitudes in response-locked ERPs (Fig 7) following the short CTI were small in young adults and larger in children and older adults. In these latter groups, MFN amplitudes were graded according to the amount of conflict presumably elicited, suggesting larger response conflict in children and older relative to young adults. For older adults a negative-going activity was evident for incongruent switch trials ~250 ms before the response. congruent incongruent non-switch homogeneous switch 5 µV + - Fig. 6 Fig.1 Fig. 2 Fig. 3Fig. 4 Fig. 5 Fig. 7 target Percentage of errors pre-response negativity children young old response 100 baseline response 100 baseline response 100 baseline FCZ MFN FCZ