Papadimitriou C, Ferdoash A, Snyder LH. Ghosts in the machine: memory interference from the previous trial. J Neurophysiol 113: 567-577, 2015. First published November 5, 2014 doi:10.1152/jn.00402.2014.-Previous memoranda can interfere with the memorization or storage of new information, a concept known as proactive interference. Studies of proactive interference typically use categorical memoranda and match-to-sample tasks with categorical measures such as the proportion of correct to incorrect responses. In this study we instead train five macaques in a spatial memory task with continuous memoranda and responses, allowing us to more finely probe working memory circuits. We first ask whether the memoranda from the previous trial result in proactive interference in an oculomotor delayed response task. We then characterize the spatial and temporal profile of this interference and ask whether this profile can be predicted by an attractor network model of working memory. We find that memory in the current trial shows a bias toward the location of the memorandum of the previous trial. The magnitude of this bias increases with the duration of the memory period within which it is measured. Our simulations using standard attractor network models of working memory show that these models easily replicate the spatial profile of the bias. However, unlike the behavioral findings, these attractor models show an increase in bias with the duration of the previous rather than the current memory period. To model a bias that increases with current trial duration we posit two separate memory stores, a rapidly decaying visual store that resists proactive interference effects and a sustained memory store that is susceptible to proactive interference. Payne et al. 1992), and language comprehension (Daneman and Carpenter 1980;Just and Carpenter 1992;Daneman and Merikle 1996), and hence an understanding of the circuitry of working memory is critical for understanding higher cognition. Spatial working memory provides an excellent model system for this purpose. The memoranda, locations in space, are continuous and well defined, as are the responses that provide a read out for these memoranda. Animals can be easily trained to perform spatial working memory tasks, and neural circuits can then be directly interrogated using various electrophysiological techniques. A number of models for working memory have been proposed (Durstewitz et al. 2000;Miyake and Shah 1999;Baddeley 2012). Here we present findings that can constrain these models and illuminate the mechanisms by which memory is degraded.Working memory may be degraded due to interference or distraction from task-irrelevant events that occur before or during the memory period. Prior computational and behavioral studies on memory interference have focused on the spatial working memory system because it provides continuous measures for both stimuli and responses and is well suited to studying partial memory degradation (Compte et al. 2000;Macoveanu et al. 2007;Chumbley et al. 2008). The...

Mooshagian E, Wang C, Ferdoash A, Snyder LH. Movement order and saccade direction affect a common measure of eye-hand coordination in bimanual reaching. J Neurophysiol 112: 730 -739, 2014. First published May 21, 2014 doi:10.1152/jn.00234.2014.-Studies of visually guided unimanual reaching have established that a saccade usually precedes each reach and that the reaction times (RTs) for the saccade and reach are highly correlated. The correlation of eye and hand RT is commonly taken as a measure of eye-hand coordination and is thought to assist visuospatial guidance of the hand. We asked what happens during a bimanual reach task. As with a unimanual reach, a saccade was executed first. Although latencies were fastest on unimanual trials, eye and hand RT correlation was identical whether just one or both hands reached to a single target. The average correlation was significantly reduced, however, when each hand reached simultaneously to a different target. We considered three factors that might explain the drop. We found that correlation strength depended on which hand reached first and on which hand reached to the same target as the saccade. Surprisingly, these two factors were largely independent, and the identity of the hand, left or right, had little effect. Eye-hand correlation was similar to that seen with unimanual reaching only when the hand that moved to the same target as the saccade was also the first hand to move. Thus both timing as well as spatial pattern are important in determining eye-hand coordination. monkey; reaction time; visually guided; visuomotor; hand movement MANUAL ACTIONS RANGING FROM the mundane, like reaching for a glass of water, to the highly skilled, like swinging a bat to hit a baseball pitched at 95 mph, rely on the spatiotemporal coordination of eyes and hand(s) for accuracy. Studies of visually guided arm and hand movements have shown that saccade and reach reaction times (RT) are positively correlated on a trial-by-trial basis (Herman et al.

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