Frini Karayanidis

Electrophysiological correlates of anticipatory and poststimulus components of task switching

Task-switching paradigms can shed light on cognitive and neural processes underlying attentional control mechanisms. An alternating runs task-switching paradigm (R. D. Rogers & S. Monsell, 1995) is used to identify ERP components associated with anticipatory and poststimulus components of task-switching processes. Subjects alternated between two tasks in a predictable series (AABB). Reaction time (RT) switch cost reduced with increasing response-stimulus (R-S) interval and a residual switch cost remained at the longest R-S interval. A switch-related positivity (D-Pos) developed in the R-S interval. D-Pos was time-locked to response onset, peaked around 400 ms post-response onset, and was unaffected by task-set interference. A switch-related negativity (D-Neg) emerged after stimulus onset. D-Neg peaked earlier with increasing R-S interval and its amplitude and latency were affected by task-set interference. D-Pos and D-Neg were interpreted within current models of task-switching.

Deviant Matters: Duration, Frequency, and Intensity Deviants Reveal Different Patterns of Mismatch Negativity Reduction in Early and Late Schizophrenia

BACKGROUND A reduction in the size of the auditory event-related potential component known as mismatch negativity (MMN) is a consistent finding in schizophrenia. This study was designed to test the hypothesis that sound intensity and duration might be more sensitive to MMN reduction early in the development of schizophrenia because of the computational complexity in extracting these two sound dimensions. METHODS The MMN elicited to sounds deviating in duration, frequency, or intensity was measured in participants with a short (n = 14, mean 2.6 years) and longer length of illness (n = 29, mean 18.9 years) relative to healthy age-matched control subjects. RESULTS For participants early in the illness, a clear reduction was evident in MMN to duration and intensity but not frequency deviants. A different pattern was observed in patients with a longer length of illness--that is, a reduction in frequency and in duration to a lesser degree but not intensity MMN. CONCLUSIONS The results indicate a pronounced age-related decline in duration and intensity MMN in control subjects that might reduce the sensitivity of these indices in schizophrenia when measured later in the course of the illness. The MMN elicited to changes in different sound properties provides potentially complementary information on the onset and progression of neuropathological changes that underlie the reduction in MMN in schizophrenia.

Advance preparation in task-switching: converging evidence from behavioral, brain activation, and model-based approaches.

Recent research has taken advantage of the temporal and spatial resolution of event-related brain potentials (ERPs) and functional magnetic resonance imaging (fMRI) to identify the time course and neural circuitry of preparatory processes required to switch between different tasks. Here we overview some key findings contributing to understanding strategic processes in advance preparation. Findings from these methodologies are compatible with advance preparation conceptualized as a set of processes activated for both switch and repeat trials, but with substantial variability as a function of individual differences and task requirements. We then highlight new approaches that attempt to capitalize on this variability to link behavior and brain activation patterns. One approach examines correlations among behavioral, ERP and fMRI measures. A second “model-based” approach accounts for differences in preparatory processes by estimating quantitative model parameters that reflect latent psychological processes. We argue that integration of behavioral and neuroscientific methodologies is key to understanding the complex nature of advance preparation in task-switching.

The spatial and temporal dynamics of anticipatory preparation and response inhibition in task-switching

We investigated ERP and fMRI correlates of anticipatory preparation and response inhibition in a cued task-switching paradigm with informatively cued, non-informatively cued and no-go trials. Cue-locked ERPs showed evidence for a multicomponent preparation process. An early cue-locked differential positivity was larger for informative vs. non-informative cues and its amplitude correlated with differential activity for informatively vs. non-informatively cued trials in the dorsolateral prefrontal cortex (DLPFC), consistent with a goal activation process. A later differential positivity was larger for informatively cued switch vs. repeat trials and its amplitude correlated with informatively cued switch vs. repeat activity in the posterior parietal cortex (PPC), compatible with a category-response (C-R) rule activation process. No-go trials elicited a frontal P3, whose amplitude was negatively correlated with activity in the ventrolateral prefrontal cortex (VLPFC) and basal ganglia motor network, suggesting that a network responsible for response execution was inhibited in the course of a no-go trial. These findings indicate that anticipatory preparation in task-switching is comprised of at least two processes: goal activation and C-R rule activation. They also support a functional dissociation between DLPFC and VLPFC, with the former involved in top-down biasing and the latter involved in response inhibition.

The many faces of preparatory control in task switching: reviewing a decade of fMRI research.

A large body of behavioural research has used the cued task‐switching paradigm to characterize the nature of trial‐by‐trial preparatory adjustments that enable fluent task implementation when demands on cognitive flexibility are high. This work reviews the growing number of fMRI studies on the same topic, mostly focusing on the central hypothesis that preparatory adjustments should be indicated by enhanced prefrontal and parietal BOLD activation in task switch when compared with task repeat trials under conditions that enable advance task preparation. The evaluation of this straight‐forward hypothesis reveals surprisingly heterogeneous results regarding both the precise localization and the very existence of switch‐related preparatory activation. Explanations for these inconsistencies are considered on two levels. First, we discuss methodological issues regarding (i) the possible impact of different fMRI‐specific experimental design modifications and (ii) statistical uncertainty in the context of massively multivariate imaging data. Second, we discuss explanations related to the multidimensional nature of task preparation itself. Specifically, the precise localization and the size of switch‐related preparatory activation might depend on the differential interplay of hierarchical control via abstract task goals and attentional versus action‐directed preparatory processes. We argue that different preparatory modes can be adopted relying either on advance goal activation alone or on the advance resolution of competition within action sets or attentional sets. Importantly, while either mode can result in a reduction of behavioral switch cost, only the latter two are supposed to be associated with enhanced switch versus repeat BOLD activation in prepared trial conditions. Hum Brain Mapp, 2013.

ERPs dissociate the effects of switching task sets and task cues

Recent studies have suggested that reaction time (RT) costs associated with switching tasks do not reflect an endogenous control process of task set reconfiguration [Logan, G. D., Bundesen, C., 2003. Clever Homunculus: Is There an Endogenous Act of Control in the Explicit Task-Cuing Procedure? J. Exp. Psychol. Hum. Percept. Perform. 29 (3), 575-599]. Participants randomly switched between two simple tasks. Task was cued 600 ms prior to stimulus presentation using either a color or shape cue. A significant RT task switch cost was found when controlling for either a repeat or switch in cue category. In comparison, a switch in cue category had no effect on RT, even when examined across a cumulative distribution. Electrophysiological data revealed early cue processing effects within the first 300 ms after cue onset. However, replicating previous findings, an increased parietal positivity was found for task switch relative to task repeat trials that emerged prior to stimulus onset. This suggests that task set reconfiguration processes are activated when switching between tasks and supports the usefulness of task-switching paradigms in investigating cognitive control processes.

Anticipatory reconfiguration elicited by fully and partially informative cues that validly predict a switch in task

Task-switching studies show no behavioral benefit of partially informative cues. However, ERP evidence of an early cue-locked positivity elicited by both fully and partially informative cues suggests that both cues trigger an anticipatory component of task set reconfiguration (Nicholson, Karayanidis, Davies, & Michie, 2006). We examined this apparent discrepancy using a cued-trials task-switching paradigm with three tasks. The ERP finding of an early cue-locked positivity was replicated for both switch-to cues, which validly predicted an upcoming switch trial and specified the new task set, and switch-away cues, which validly predicted an upcoming switch trial but not the new task set. This component was not elicited by a noninformative cue that did not specify whether the task would switch or repeat. Switch-away cues resulted in more accurate but not faster responding than did noninformative cues. Modeling of decision processes confirmed a speed-accuracy trade-off between these conditions and a preparation benefit for both switch-to and switch-away cues. These results indicate that both fully and partially informative cues elicit an early anticipatory component of task set reconfiguration that is reflected in the early cue-locked positivity. We argue that the pattern of results is most consistent with a task set inhibition account of this early anticipatory component of task set reconfiguration.

The effect of clozapine therapy on frontal lobe dysfunction in schizophrenia: neuropsychology and event-related potential measures

There are several reports that performance-based measures as well as symptom ratings improve with clozapine in patients with schizophrenia who previously responded poorly to typical neuroleptic treatment. It is not clear whether improved cognitive function following initiation of clozapine is simply related to relief of psychotic symptoms and extrapyramidal side-effects associated with prior use of typical neuroleptics, or reflects another dimension of the greater efficacy of clozapine compared with typical neuroleptics. To elucidate this issue and better specify the cognitive changes associated with use of clozapine, the authors have assessed cognitive function psychometrically and using event-related potentials (ERPs), pre- and 8-12 wk post-initiation of clozapine treatment. Patients were rated on the BPRS, the SAPS and the SANS and completed a number of tests tapping aspects of frontal lobe function. ERP recordings were conducted using an auditory task twice, which was repeated under passive and active attention conditions. It was found that clozapine differentially affects tests reflecting executive and planning function, and not stimulus-driven cognitive functions. The results were not consistent with the hypothesis that these effects were simply due to relief of medication side-effects but could be related to the D(1) receptor antagonist actions of clozapine.

Adjustments of response threshold during task switching: a model-based functional magnetic resonance imaging study

Adjustment of response threshold for speed compared with accuracy instructions in two-choice decision-making tasks is associated with activation in the fronto-striatal network, including the pre-supplementary motor area (pre-SMA) and striatum (Forstmann et al., 2008). In contrast, increased response conservativeness is associated with activation of the subthalamic nucleus (STN) (Frank et al., 2007). We investigated the involvement of these regions in trial-by-trial adjustments of response threshold in humans, using a cued-trials task-switching paradigm. Fully and partially informative switch cues produced more conservative thresholds than repeat cues. Repeat cues were associated with higher activation in pre-SMA and striatum than switch cues. For all cue types, individual variability in response threshold was associated with activation level in pre-SMA, with higher activation linked to lower threshold setting. In the striatum, this relationship was found for repeat cues only. These findings support the notion that pre-SMA biases the striatum to lower response threshold under more liberal response regimens. In contrast, a high threshold for switch cues was associated with greater activation in right STN, consistent with increasing response caution under conservative response regimens. We conclude that neural models of response threshold adjustment can help explain executive control processes in task switching.

Event-related potentials associated with masked priming of test cues reveal multiple potential contributions to recognition memory

The relationship between recognition memory and repetition priming remains unclear. Priming is believed to reflect increased processing fluency for previously studied items relative to new items. Manipulations that affect fluency can also affect the likelihood that participants will judge items as studied in recognition tasks. This attribution of fluency to memory has been related to the familiarity process, as distinct from the recollection process, that is assumed by dual-process models of recognition memory. To investigate the time courses and neural sources of fluency, familiarity, and recollection, we conducted an event-related potential (ERP) study of recognition memory using masked priming of test cues and a remember/know paradigm. During the recognition test, studied and unstudied words were preceded by a brief, masked word that was either the same or different. Participants decided quickly whether each item had been studied (old or new), and for items called old, indicated whether they remembered (R) the encoding event, or simply knew (K) the item had been studied. Masked priming increased the proportion of K, but not R, judgments. Priming also decreased response times for hits but not correct rejections (CRs). Four distinct ERP effects were found. A medial-frontal FN400 (300500 msec) was associated with familiarity (R, K Hits > CRs) and a centro-parietal late positivity (500800 msec) with recollection (R Hits > K Hits, CRs). A long-term repetition effect was found for studied items judged new (Misses > CRs) in the same time window as the FN400, but with a posterior distribution. Finally, a centrally distributed masked priming effect was visible between 150 and 250 msec and continued into the 300500 msec time window, where it was topographically dissociable from the FN400. These results suggest that multiple neural signals are associated with repetition and potentially contribute to recognition memory.