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. © 2011 Wiley Periodicals, Inc.     

Electrophysiological correlates of anticipatory task-switching processes

Recent studies show a differential switch-related positivity emerging before a switch trial and reflecting anticipatory task-set reconfiguration processes. In this study, the switch-related positivity was examined in a cued task-switching paradigm. Cue-stimulus and response-stimulus intervals were independently manipulated to dissociate between the effects of anticipatory preparation and passive dissipation of task-set interference. Reaction time switch cost declined with increasing cue-stimulus and response-stimulus intervals, suggesting a contribution from both active preparation and passive interference processes. In cue-related difference waveforms, a switch positivity peaked around 350-400 ms and is interpreted as reflecting differential activation of task-set reconfiguration. In stimulus-related difference waveforms, a switch-related negativity is believed to indicate the role of S-R priming and response interference in task-switching.     

Components of task-set reconfiguration: differential effects of 'switch-to' and 'switch-away' cues

Preparation for a switch in task was manipulated using two types of switch cues: 'switch-away' from the previous task-set and 'switch-to' a different task-set. Increasing cue-stimulus interval resulted in a reduction in reaction time switch cost for switch-to trials only. Cue-locked difference waveforms for both switch-to and switch-away trials showed a large, broad differential positivity, relative to repeat waveforms. However, the later part of the differential positivity was significantly reduced on switch-away trials. A differential positivity then emerged after stimulus onset for switch-away trials only. This suggests that, with a long cue-stimulus interval, the new task-set was implemented before stimulus onset for switch-to trials, whereas on switch-away trials this process was delayed until after stimulus onset leading to increased switch cost. These results demonstrate dissociable effects of switching away from the current task-set and switching to the upcoming task-set and support the interpretation that the differential positivity observed for switch-to trials reflects processes associated with anticipatory task-set reconfiguration.     

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.     

Auditory event-related potential indices of fronto-temporal information processing in schizophrenia syndromes: valid outcome prediction of clozapine therapy in a three-year follow-up

Reliability, specificity, and validity of three event-related potential (ERP) indices of non-attended and attended auditory information processing [the mismatch negativity (MMN), the novelty-P3a and the target-P3b] were assessed in 21 healthy subjects and 25 schizophrenic patients while performing a visual discrimination task (Ignore condition) and, subsequently, an auditory discrimination task (Attend condition). Re-test reliability, as measured in a subset of 10 healthy subjects and 9 patients respectively, ranged from r=0.4 to r=0.8. In both groups P3a was found to be smaller in the Ignore than in the Attend condition. Patients had significantly larger P3a amplitudes than healthy subjects while their MMN and P3b amplitudes were smaller. Two ERP factors were extracted in healthy subjects: (1) 'novelty reaction' with high loading scores for P3a and (2) 'deviant detection' with high loading scores for MMN. P3b was predominantly loading on the first factor thus confirming partly overlapping P3a and P3b generators. However, considerable variance was also shared by the second factor, particularly in patients. External validity of the ERP factors was confirmed post hoc. Particularly ERP indices of deviant detection were found to be associated with negative symptoms. In order to assess further clinical relevance, therapy response to clozapine was followed-up over 3 yr in a sub-sample of 17 patients. Poor treatment response was associated with high Novelty Factor scores and large P3a amplitudes whereas good response was associated with high Deviant Factor scores and relatively intact MMN. It is concluded that ERP abnormalities provide a severity index of brain impairment and a measure of predicting therapeutic outcome.     

Arthritis of the hip in spondylarthorpathy: retrospective study about 126 cases

PURPOSE: To determine epidemiological and clinical features of arthritis of the hip in a Tunisian population of spondylarthrpathy (SA). PATIENTS AND METHODS: This is a retrospective study about patients suffering from SA treated in a rheumatology unit. A radiological investigation of the pelvis was systematically performed on each patient. RESULTS: The study in involved 126 cases of SA (83 men and 43 women), with a middle age of 32.6 years. Arthritis of the hip showed within 3.8 years. Total hip arthroplasty was indicated in 18% of cases. Arthritis of the hip in spondylarthropathy is an important cause of functional disability. We insist in our study on the frequency of arthritis of the hip in North Africa and particularly in patients aged under 16 years.     

A voluminous foraminal and extra foraminal disk hernia mimicking a tumor

In some cases, disc herniation can be voluminous and can then constitute a differential diagnosis with tumours. We report the case of a 46 years-old female with sciatica and crural neuralgia which resisted to medical treatment. X-rays exams were normal, but the computerized tomography showed a voluminous mass in contact with the L5 nervous root and which was developed in the psoas major muscle. The MRI revealed a voluminous foraminal and extra foraminal herniation at the L4-L5 vertebral disc, extended up to the psoas major muscle and associated with an important inflammatory infiltration. Surgical treatment was successful with a follow up of 8 months.     

Disrupted sensory gating in pathological gambling.

BACKGROUND: Some neurochemical evidence as well as recent studies on molecular genetics suggest that pathologic gambling may be related to dysregulated dopamine neurotransmission. METHODS: The current study examined sensory (motor) gating in pathologic gamblers as a putative measure of endogenous brain dopamine activity with prepulse inhibition of the acoustic startle eye-blink response and the auditory P300 event-related potential. Seventeen pathologic gamblers and 21 age- and gender-matched healthy control subjects were assessed. Both prepulse inhibition measures were recorded under passive listening and two-tone prepulse discrimination conditions. RESULTS: Compared to the control group, pathologic gamblers exhibited disrupted sensory (motor) gating on all measures of prepulse inhibition. Sensory motor gating deficits of eye-blink responses were most profound at 120-millisecond prepulse lead intervals in the passive listening task and at 240-millisecond prepulse lead intervals in the two-tone prepulse discrimination task. Sensory gating of P300 was also impaired in pathologic gamblers, particularly at 500-millisecond lead intervals, when performing the discrimination task on the prepulse. CONCLUSIONS: In the context of preclinical studies on the disruptive effects of dopamine agonists on prepulse inhibition, our findings suggest increased endogenous brain dopamine activity in pathologic gambling in line with previous neurobiological findings.     

Microstructural white matter changes mediate age‐related cognitive decline on the Montreal Cognitive Assessment (MoCA)

Although the relationship between aging and cognitive decline is well established, there is substantial individual variability in the degree of cognitive decline in older adults. The present study investigates whether variability in cognitive performance in community‐dwelling older adults is related to the presence of whole brain or tract‐specific changes in white matter microstructure. Specifically, we examine whether age‐related decline in performance on the Montreal Cognitive Assessment (MoCA), a cognitive screening tool, is mediated by the white matter microstructural decline. We also examine if this relationship is driven by the presence of cardiovascular risk factors or variability in cerebral arterial pulsatility, an index of cardiovascular risk. Sixty‐nine participants (aged 43–87) completed behavioral and MRI testing including T1 structural, T2‐weighted FLAIR, and diffusion‐weighted imaging (DWI) sequences. Measures of white matter microstructure were calculated using diffusion tensor imaging analyses on the DWI sequence. Multiple linear regression revealed that MoCA scores were predicted by radial diffusivity (RaD) of white matter beyond age or other cerebral measures. While increasing age and arterial pulsatility were associated with increasing RaD, these factors did not mediate the relationship between total white matter RaD and MoCA. Further, the relationship between MoCA and RaD was specific to participants who reported at least one cardiovascular risk factor. These findings highlight the importance of cardiovascular risk factors in the presentation of cognitive decline in old age. Further work is needed to establish whether medical or lifestyle management of these risk factors can prevent or reverse cognitive decline in old age.