Hot off the presses! Jun 01 Neuropsychologia

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Latest Articles Include:

• Editorial Board
  - Neuropsychologia 47(7):CO2 (2009)
  
• The effect of non-visual working memory load on top-down modulation of visual processing
  - Neuropsychologia 47(7):1637-1646 (2009)
  While a core function of the working memory (WM) system is the active maintenance of behaviorally relevant sensory representations, it is also critical that distracting stimuli are appropriately ignored. We used functional magnetic resonance imaging to examine the role of domain-general WM resources in the top-down attentional modulation of task-relevant and irrelevant visual representations. In our dual-task paradigm, each trial began with the auditory presentation of six random (high load) or sequentially ordered (low load) digits. Next, two relevant visual stimuli (e.g., faces), presented amongst two temporally interspersed visual distractors (e.g., scenes), were to be encoded and maintained across a 7-s delay interval, after which memory for the relevant images and digits was probed. When taxed by high load digit maintenance, participants exhibited impaired performance on the visual WM task and a selective failure to attenuate the neural processing of task-irreleva! nt scene stimuli. The over-processing of distractor scenes under high load was indexed by elevated encoding activity in a scene-selective region-of-interest relative to low load and passive viewing control conditions, as well as by improved long-term recognition memory for these items. In contrast, the load manipulation did not affect participants' ability to upregulate activity in this region when scenes were task-relevant. These results highlight the critical role of domain-general WM resources in the goal-directed regulation of distractor processing. Moreover, the consequences of increased WM load in young adults closely resemble the effects of cognitive aging on distractor filtering [Gazzaley, A., Cooney, J. W., Rissman, J., & D'Esposito, M. (2005). Top-down suppression deficit underlies working memory impairment in normal aging. Nature Neuroscience 8, 1298–1300], suggesting the possibility of a common underlying mechanism.
• Control of visually guided saccades in multiple sclerosis: Disruption to higher-order processes
  - Neuropsychologia 47(7):1647-1653 (2009)
  Ocular motor abnormalities are a common feature of multiple sclerosis (MS), with more salient deficits reflecting tissue damage within brainstem and cerebellar circuits. However, MS may also result in disruption to higher level or cognitive control processes governing eye movement, including attentional processes that enhance the neural processing of behaviourally relevant information. The attentional control of eye movement was investigated in 25 individuals with MS and a comparable number of neurologically healthy individuals matched for age and IQ. This entailed an evaluation of distractor-related effects on the generation of both unpredictable and predictable visually guided saccades, as well as an evaluation of the effects of presenting endogenous cues prior to target onset. For unpredictable saccades, we revealed an exaggerated distractor effect in MS, with saccade latencies prolonged and endpoints less accurate in the presence of a visual distractor. Predictable! saccades tended to be hypometric for MS patients, although we found no significant distractor effects. For endogenously cued saccades, we found no group differences in latency following a valid cue, but an exaggerated increase in latency following invalid cues for MS patients. MS patients also generated a significantly greater proportion of erroneous responses to cue stimuli. These ocular motor characteristics demonstrate considerable sensitivity with respect to evaluating attentional deficits in MS, evident even in the absence of clinical signs of disease.
• Cognitive and emotional processing in high novelty seeking associated with the L-DRD4 genotype
  - Neuropsychologia 47(7):1654-1659 (2009)
  The personality trait of novelty seeking (NS) has been associated with the long variant of the dopamine D4 receptor (L-DRD4) VNTR polymorphism. This is the first study to examine the influence of L-DRD4 polymorphism on some of the cognitive (i.e. decision making) and emotional underpinnings of the NS phenotype. One hundred and eighteen healthy males grouped in a L-DRD4 (n = 24) and a S-DRD4 (n = 94) group, completed multimodal assessment for personality, planning for problem solving and decision making. Two age-matched L-DRD4 and S-DRD4 sub-samples (n = 17 each) entered and completed emotional processing using startle modulation by affective pictures. ANOVAs showed that L-DRD4 individuals had higher NS, made more risky choices and won less money in the decision making task, but had intact planning for problem solving. They also had reduced startle reactivity and late startle modulation by both pleasant and unpleasant pictures. Early, attentional startle modulation by t! he affective pictures was intact. NS correlated negatively with startle reactivity and performance in the emotional decision task. These results suggest that the L-DRD4 polymorphism is associated with high NS and risk taking, under-reactivity to unconditioned aversive stimuli, constricted emotional responses but preserved attentional processing of emotional stimuli and efficient problem solving. These results extend animal evidence on DRD4-mediated control of decision making and emotional processing to humans. The proposed role of the NS phenotype in human evolution and in disorders of impulsivity is discussed under the light of the present findings.
• Frontal lobe involvement in a task of time-based prospective memory
  - Neuropsychologia 47(7):1660-1669 (2009)
  Time-based prospective memory (PM) has been found to be negatively affected by aging, possibly as a result of declining frontal lobe (FL) function. Despite a clear retrospective component to PM tasks, the medial temporal lobes (MTL) are thought to play only a secondary role in successful task completion. The present study investigated the role of the FLs and MTLs in time-based PM, as well as their involvement in clock monitoring, plan generation, and time estimation, each of which may play a role in the execution of time-based PM tasks. Based upon their scores on composite measures of FL and MTL function, 32 older adults were divided into four groups, and were then tested on a time-based laboratory PM task. Overall age effects were also assessed and each of the four groups was compared to a group of 32 younger adults. High-frontal functioning participants demonstrated better prospective memory than low-frontal functioning participants, and were not distinguishable from! younger adults. Older adults with high-MTL scores performed significantly better than those with low-MTL scores, but only if they were also high in FL function. FL function, but not MTL function, predicted patterns of clock monitoring, quality of plans generated to assist in time-based PM performance, and the accuracy of time estimation. Again, on each of these measures the performance of the high-frontal group was equivalent to that of the younger adults. The results of this study suggest that it is not aging per se that disrupts PM performance, but it is instead primarily the diminished frontal function seen in a subset of older adults.
• Attention, intention, and strategy in preparatory control
  - Neuropsychologia 47(7):1670-1685 (2009)
  The neural mechanisms underlying different forms of preparatory control were examined using event-related fMRI. Preparatory brain activation was monitored in relation to different types of advance information: (1) random task cues indicating which of two possible tasks to perform upon subsequent target presentation; (2) task-ambiguous target stimuli; or (3) targets for which the correct response could be pre-determined. Three types of activation pattern were observed in different brain regions. First, more posterior regions of lateral prefrontal cortex (LPFC) and parietal cortex were activated by both advance task cues and advance targets, but with increased and more sustained activation for the latter. Second, more anterior regions of LPFC and parietal cortex were selectively activated by advance targets. Importantly, in these regions preparatory activation was not further modulated by the availability of advance response information. In contrast, preparatory activati! on in a third set of brain regions, including medial frontal cortex, reflected the utilization of advance response information, but by only a subset of participants. These results suggest three types of preparatory control: attentional (stimulus-oriented), intentional (action-oriented), and a possibly strategic component that might determine inter-individual differences in response readiness. Notably, the absence of regions selectively or even preferentially activated during cue-based preparation argues against certain conceptualizations of task-selective attention under cued task-switching conditions.
• Declarative memory is critical for sustained advantageous complex decision-making
  - Neuropsychologia 47(7):1686-1693 (2009)
  Previous studies have reported conflicting evidence concerning the contribution of declarative memory to advantageous decision-making on the Iowa Gambling Task (IGT). One study, in which the measurement of psychophysiology during the task necessitated a 10-s delay between card selections, found that six participants with amnesia due to hippocampal damage failed to develop a preference for advantageous decks over disadvantageous decks [Gutbrod, K., Krouzel, C., Hofer, H., Muri, R., Perrig, W., & Ptak, R. (2006). Decision-making in amnesia: Do advantageous decisions require conscious knowledge of previous behavioural choices? Neuropsychologia, 44(8), 1315–1324]. However, a single-case study (where psychophysiology was not measured and no delay between card selections occurred) showed that an amnesic patient developed normal preference for advantageous decks [Turnbull, O. H., & Evans, C. E. (2006). Preserved complex emotion-based learning in amnesia. Neuropsychologia, 4! 4(2), 300–306]. We sought to resolve these discrepant findings by examining IGT performances in five patients with profound amnesia (WMS-III General Memory Index M = 63) and bilateral hippocampal damage caused by anoxia (n = 4) or herpes simplex encephalitis (n = 1). In one administration of the IGT, psychophysiology measurements were utilized and a 6-s delay was interposed between card selections. In a second administration, no delay between card selections was interposed. While age-, sex-, and education-matched healthy comparison participants showed significant learning with a gradual preference for advantageous decks in both conditions, amnesic patients, irrespective of IGT administration condition and extent of medial temporal lobe damage, failed to develop this preference. These findings strongly discount the possibility that the delay between card selections explains why amnesic participants fail to learn in the IGT, and suggest instead a significant role for medial! temporal lobe declarative memory systems in the type of compl! ex decision-making tapped by the IGT.
• Space-based but not object-based inhibition of return is impaired in Parkinson's disease
  - Neuropsychologia 47(7):1694-1700 (2009)
  Impairments in certain aspects of attention have frequently been reported in Parkinson's disease (PD), including reduced inhibition of return (IOR). Recent evidence suggests that IOR can occur when attention is directed at objects or locations, but previous investigations of IOR in PD have not systematically compared these two frames of reference. The present study compared the performance of 18 nondemented patients with PD and 18 normal controls on an IOR task with two conditions. In the "object-present" condition, objects surrounded the cues and targets so that attention was cued to both a spatial location and to a specific object. In the "object-absent" condition, surrounding objects were not presented so that attention was cued only to a spatial location. When participants had to rely on space-based cues, PD patients demonstrated reduced IOR compared to controls. In contrast, when objects were present in the display and participants could use object-based c! ues, PD patients exhibited normal IOR. These results suggest that PD patients are impaired in inhibitory aspects of space-based attention, but are able to overcome this impairment when their attention can be directed at object-based frames of reference. This dissociation supports the view that space-based and object-based components of attention involve distinct neurocognitive processes.
• Unilateral damage to the right cerebral hemisphere disrupts the apprehension of whole faces and their component parts
  - Neuropsychologia 47(7):1701-1711 (2009)
  Although most cases of acquired prosopagnosia are accompanied by bilateral brain lesions, a number also arise following right unilateral lesions. The prevailing consensus is that right hemisphere damage disrupts the configural apprehension of faces, which in turn forces a reliance on part-based processing. Here we describe a patient who following right hemisphere damage is not only unable to apprehend the configural aspects of faces, but is also unable to apprehend their component parts when these are presented within a whole, upright face. Intriguingly, the patient is able to apprehend face parts when these are presented in isolation, within inverted faces, or in unfamiliar, scrambled arrangements. Furthermore, the patient can make use of configural information to detect local changes in non-face stimuli. The findings uncover a hitherto unreported form of impairment following right unilateral damage, and raise questions about the role of the left hemisphere in process! ing local information.
• Adaptation of eye-movements to simulated hemianopia in reading and visual exploration: Transfer or specificity?
  - Neuropsychologia 47(7):1712-1720 (2009)
  Reading and visual exploration impairments in unilateral homonymous hemianopia are well-established clinical phenomena. Spontaneous adaptation of eye-movements to the visual field defect leads to improved reading and visual exploration performance. Yet, it is still unclear whether oculomotor adaptation to visual field loss is task-specific or whether there is a transfer of adaptation-related improvements between reading and visual exploration. We therefore simulated unilateral homonymous hemianopia in healthy participants and explored the specificity with which oculomotor adaptation to this pure visual-sensory dysfunction during uninstructed reading or visual exploration practice leads to improvements in both abilities. Our findings demonstrate that there is no transfer of adaptation-related changes of eye-movements and performance improvements between reading and visual exploration. Efficient oculomotor adaptation to visual field loss is highly specific and task-depen! dent.
• Evidence for long-range feedback in target detection: Detection of semantic targets modulates activity in early visual areas
  - Neuropsychologia 47(7):1721-1727 (2009)
  In a variety of attention and search tasks, single-cell recordings of the primate brain have frequently shown an enhancement of responses in early visual areas to selected target stimuli. This enhancement is observed only at longer latencies, suggesting the possibility that it reflects the action of feedback or return signals from upstream processing areas. However, in typical studies, targets are specified on the basis of elementary visual features; as these are coded at multiple levels of the visual system, it is impossible to determine where enhanced target processing begins. Using human functional magnetic resonance imaging (fMRI), we demonstrate enhancement of activity in early visual areas even when low-level visual information is insufficient for target detection to occur. We found enhanced activity in early visual areas to targets defined purely by semantic category, suggesting that feedback signals returning from at least as far forward as temporal lobe semant! ic processing can influence visual responses. These findings also suggest feedback signaling as a mechanism by which early and late brain systems coding for different properties of a target object can integrate their activity, allowing for the target object to dominate overall processing.
• Cross-sensory gating in schizophrenia and autism spectrum disorder: EEG evidence for impaired brain connectivity?
  - Neuropsychologia 47(7):1728-1732 (2009)
  Autism spectrum disorders (ASD) and schizophrenia are both neurodevelopmental disorders that have extensively been associated with impairments in functional brain connectivity. Using a cross-sensory P50 suppression paradigm, this study investigated low-level audiovisual interactions on cortical EEG activation, which provides crucial information about functional integrity of connections between brain areas involved in cross-sensory processing in both disorders. Thirteen high functioning adult males with ASD, 13 high functioning adult males with schizophrenia, and 16 healthy adult males participated in the study. No differences in neither auditory nor cross-sensory P50 suppression were found between healthy controls and individuals with ASD. In schizophrenia, attenuated P50 responses to the first auditory stimulus indicated early auditory processing deficits. These results are in accordance with the notion that filtering deficits may be secondary to earlier sensory dysfu! nction. Also, atypical cross-sensory suppression was found, which implies that the cognitive impairments seen in schizophrenia may be due to deficits in the integrity of connections between brain areas involved in low-level cross-sensory processing.
• Visuoperceptual deficits in letter-by-letter reading?
  - Neuropsychologia 47(7):1733-1744 (2009)
  A longstanding and controversial issue concerns the underlying mechanisms that give rise to letter-by-letter (LBL) reading: while some researchers propose a prelexical, perceptual basis for the disorder, others postulate a postlexical, linguistic source for the problem. To examine the nature of the deficit underlying LBL reading, in three experiments, we compare the performance of seven LBL readers, matched control participants and one brain-damaged patient, OL, with no reading impairment. Experiment 1 revealed that the LBL patients were impaired, relative to the controls and to OL, on a same/different matching task using checkerboards of black and white squares. Given that the perceptual impairment extends beyond abnormalities with alphanumeric stimuli, the findings are suggestive of a more general visual processing deficit. This interpretation was confirmed in Experiments 2 (matching words and symbol strings) and 3 (visual search of letter and symbol targets), which ! compared the processing of linguistic and non-linguistic written stimuli, matched for visual complexity. In both experiments, the LBL patients displayed qualitatively similar effects of length and left-to-right sequential ordering on linguistic and non-linguistic stimuli. Moreover, there was a clear association between the perceptual impairments on these tasks and the slope of the reading latency function for the LBL patients. Taken together, these findings are consistent with a significant visuoperceptual impairment in LBL that adversely affects reading performance as well as performance on other non-reading tasks.
• Heterotopagnosia: When I point at parts of your body
  - Neuropsychologia 47(7):1745-1755 (2009)
  Heterotopagnosia is the acquired inability of brain-lesioned patients to point at someone else's body parts when prompted. The cognitive basis of this disorder is unclear. It might result from a biological function deficit critical for communication in human beings; alternatively, it could result from the disruption of a body representation. Here, we report three patients with heterotopagnosia following a recent left parieto-occipital stroke and a previous insular lesion. The patients were tested on their ability to name, point out and grasp several targets including body parts (own, real others' and figurative others'). Language, visuo-spatial deficits or any confounding neuropsychological disorders were controlled for. We found that the patients erroneously pointed to their own body parts when asked to point at someone else's. Strikingly, their ability to grasp someone else's body parts was largely unimpaired. The dissociation between their grasping and communica! tive pointing abilities supports the hypothesis that heterotopagnosia is a disorder of communicative function conveyed by pointing but not by grasping. In addition, pointing performance in our patients varied according to the target: the more similar the target was to a real person, the worse the patients' pointing performance. We suggest that communicative pointing might require a specific representation of the addressee's body and point of view, a heterocentric representation. In the patients described here this phenomenon resulted from a combined insulo-parietal lesion, which may explain why, in contrast to other patients described previously, the heterotopagnosia was long-lasting.
• Distractibility with advancing age and Parkinson's disease
  - Neuropsychologia 47(7):1756-1764 (2009)
  Focused attention can be compromised by the neurodegenerative processes associated with both healthy aging and Parkinson's disease (PD). Deficits in ignoring distractors with reflexive or overlearned response links have been attributed to impaired inhibition. The current research assessed whether similar deficits occur for distractors with recently learned arbitrary response associations, for which sensorimotor transformations are far less automatic and therefore considerably easier to resist. We used a selective attention task that evaluated distractibility and the use of distractor inhibition within the same context. The task involved stimuli that were arbitrarily assigned to responses based on a rule learned during the testing session. Performance showed that distraction increased with both healthy aging and PD. Moreover, these increases in distraction were accompanied by decreases in overt evidence of distractor inhibition, which appear to reflect at least in part ! a failure of reactive inhibition. Comparison of the deficits in the two groups indicates that the key difference reflects severity, rather than distinct symptoms, suggesting that they stem from neural changes associated with both aging and PD. These results demonstrate that aging- and PD-related hyper-distractibility and impaired inhibition during focused attention affect stimuli without prepotent response links, which implicates dopaminergic networks in the strategic control of arbitrary visuomotor transformations.