RECENT PRESENTATIONS

Gevins, A., Smith, M.E., McEvoy, L.K., & Ilan, A. (2003). EEG and ERP signals of working memory. International Society for Brain Electromagnetic Topography, November, Santa Fe, NM.

ABSTRACT

Working memory, the conscious effortful process of maintaining & manipulating representations (information) in one's mind for several seconds, is arguably the most fundamental of higher cognitive brain functions. WM involves a hypothetical limited capacity "Central Executive" system and task-specific representational processing systems. Neuroimaging studies of WM tasks show activation of dorsolateral & medial prefrontal and parietal cortex, as well as task-specific areas. Our lab has studied EEG & ERP signals of WM since the mid '80s using the n-back task in which a remembered stimulus, such as a letter or its position on the screen, is compared with a new stimulus (Gevins et al., 1990). (The n in n-back refers to how many trials back the remembered stimulus is.) This task is well controlled in that stimulus and response factors can be held constant while varying task difficulty and type of information. The n-back task evokes well-known EEG & ERP signals (Gevins et al., 1990, 1996, 1997). The magnitude of the continuous load on the attentional resources available for maintaining information in working memory during the n-back task can be measured with frequency domain parameters of the ongoing EEG such as frontal and parietal alpha band power and frontal midline theta band power. ERP peak amplitudes and latencies are modulated by the transient allocation of attention to stimulus processing during the n-back task, in particular the competition between the concurrent demands to maintain and update information while evaluating and responding to new stimuli. The main ERP signals modulated by WM tasks are CNV, P250, P300 and Slow Waves (McEvoy, Smith & Gevins, 1998). These EEG & ERP WM signals are stable after practice (Smith, McEvoy & Gevins 1999), have high test-retest reliability (r>.90; p < .001) (McEvoy, Smith & Gevins, 2000), and their modulation is consistent from childhood to old age (Pellouchoud, Smith, McEvoy & Gevins, 1999; McEvoy, Pellouchoud, Smith & Gevins, 2001). The signals have high face validity in that their modulation by variations in task difficulty can be accurately measured in individual subjects (>90%; p < .001) (Gevins, Smith, Leong, McEvoy, et al, 1998). They have high construct validity in that differences between people in WM task performance & EEG & ERP signals are good predictors of a well-known measure of individual differences in cognitive ability, the Wechsler Adult Intelligence Scale IQ score (multiple R=.80; p < .001) (Gevins & Smith, 2000). Finally, they have high discriminative validity in the sense that the n-back WM task and associated EEG & ERP signals are highly sensitive to transient & chronic changes in neurocognitive function due to a variety of stressors including: antihistamines, caffeine, alcohol & marijuana (Gevins & Smith, 1999; Gevins et al., 2001; Gevins, Smith & McEvoy, 2002; Ilan & Gevins, 2001; Ilan, Smith & Gevins, Submitted), anti-epileptic drugs (Chung et al, 2002; Gevins, Meador, et al, In Prep.), and extended Wakefulness (Smith, McEvoy & Gevins, 2002). Together, this body of research results suggests that a clinical neurophysiological test of working memory is scientifically feasible. Supported by grants from the NIMH, NINDS, NIA, NICHHD, NIAAA, NIDA & NHLBI.