Time course of evoked-potential changes in different forms of anomia in aphasia

No abstract available

Reflexive Orienting in Spatial Neglect Is Biased towards Behaviourally Salient Stimuli

Patients with spatial neglect are impaired when detecting contralesional targets presented shortly after an ipsilesional cue. This ‘disengagement' deficit is believed to reflect reflexive orienting towards ipsilesional stimuli that is independent of behavioural goals. Here, we show that the extent of this spatial bias depends on the behavioural salience of ipsilesional stimuli. Healthy participants, brain-injured patients without neglect and neglect patients reacted to ipsilesional and contralesional visual targets. Prior to target presentation, a visual cue similar or dissimilar to the target was presented at target position or opposite the target. Although participants did not react to the similar cue, it had high behavioural salience since it shared features with the target stimulus. Neglect patients showed dramatically increased reaction times to contralesional targets, but only when these followed behaviourally relevant ipsilesional cues. No decrease of performance was observed with irrelevant cues. This performance pattern was not due to perceptual similarity, since the same effect was found when cue and target were semantically related but differed perceptually. Importantly, semantically related cues ceased to attract attention when they were defined as behaviourally irrelevant. These results show that neglect patients only orient attention reflexively towards ipsilesional stimuli with high behavioural salienc

Iron-Deficiency Anemia as a Rare Cause of Cerebral Venous Thrombosis and Pulmonary Embolism

Cerebral venous thrombosis (CVT) is a relatively rare cause of stroke and has a wide spectrum of unspecific symptoms, which may delay diagnosis. There are many etiologies, including hematological disorders, trauma, infection, and dehydration. Iron-deficiency anemia (IDA) has been reported as an extremely rare cause of CVT, especially in adults

ERP correlates of word production before and after stroke in an aphasic patient

No abstract available

Subcortical loop activation during selection of currently relevant memories

Clinical studies on spontaneous confabulation and imaging studies with healthy subjects indicate that the anterior limbic system, in particular, the orbitofrontal cortex (OFC), is necessary to adjust thought and behavior to current reality. It appears to achieve this by continuously suppressing activated memories that do not pertain to ongoing reality, even before their content is consciously recognized. In the present study, we explored through what anatomical connections the OFC exerts this influence. Healthy subjects were scanned with H(2)(15)O PET as they performed four blocks of continuous recognition tasks, each block composed of a different type of stimuli (meaningful designs, geometric designs, words, nonwords). Within each block, three runs composed of exactly the same picture series, arranged in different order each time, were made. Subjects were asked to indicate item recurrences only within the currently ongoing run and to disregard familiarity from previous runs. In the combined first runs, in which all items were initially new and responses could be based on familiarity judgement (with repeated items) alone, we found medial temporal and right orbitofrontal activation. In the combined third runs, when all items were already known and selection of currently relevant memories was required, we found left orbitofrontal activation contingent with distinct activation of the ventral striatum, head and body of the caudate nucleus, substantia nigra, and medial thalamus. The study indicates that the OFC influences the cortical representation of memories through subcortical connections including the basal ganglia and the thalamus. The data are compatible with a role of the dopaminergic reward system in the monitoring of ongoing reality in thinking

The mechanisms of spontaneous and provoked confabulations

Summary Confabulation is a mysterious adjunct of amnesia. It remains unexplained why some patients invent untrue stories in response to questions (provoked confabulations) or even spontaneously with no apparent motivation (spontaneous confabulations). Hypothesized mechanisms range from a desire to fill gaps in memory to a loss of the temporal context in memory. We examined the mechanisms of confabulations in 16 amnesic patients. Patients were classified as spontaneous confabulators if they ever acted according to their confabulations. Provoked confabulations were measured as the number of intrusions in a verbal learning test. We found a double dissociation between the two types of confabulations, indicating that they represent different disorders rather than different degrees of the same disorder. Confabulating patients did not show an increased tendency to fill gaps in memory as measured by the number of fake questions concerning non existent items that they answered. Neither type of confabulation correlated with a failure to store new information as gauged with recognition tasks; pure information storage was even found to be normal in some patients. However, we found a positive correlation between several measures of verbal learning and verbal fluency with provoked, but not spontaneous, confabulations. In contrast, spontaneous, but not provoked, confabulations were associated with an inability to recognize the temporal order of stored information as measured by the comparison of two runs of a continuous recognition task. We suggest that provoked confabulations depend on an amnesic subject's search in his deficient memory and are the trade-off for increased item recollection. Spontaneous confabulations appear to be based on a failure to recognize the temporal order of stored information, resulting in erroneous recollection of elements of memory that do not belong togethe

Disorientation in amnesia: A confusion of memory traces

Disorientation is a common phenomenon in delirium and amnesia. It is thought to have an obvious explanation, i.e. disoriented patients fail to store the information crucial for the maintenance of orientation. In this study, we explored whether disorientation was indeed associated with a failure to learn new information or rather with a confusion of information within memory. Twenty-one patients with severe amnesia were examined. Orientation was tested with a 20item questionnaire. Two runs of a continuous recognition task were used to test the ability to acquire information (first run of the task) and the tendency to confuse the temporal context of information acquisition (comparison of the second with the first run). We found that orientation was much better predicted by the measure of temporal context confusion (r = 0.90) than by the ability to simply acquire information (r = 0.54). Superimposition of neuroradiological scans demonstrated that increased temporal context confusion was associated with medial orbitofrontal or basal forebrain damage; patients with normal levels of temporal context confusion did not have damage to these areas. We conclude that disorientation more often indicates a confusion of memory traces from different events, i.e. increased temporal context confusion, than an inability to learn new information. Disorientation appears to reflect primarily a failure of the orbitofrontal contribution to memor

A non-spatial bias favouring fixated stimuli revealed in patients with spatial neglect

The cardinal feature of spatial neglect is severely impaired exploration of the contralesional space, a failure resulting in unawareness of many contralesional stimuli. This deficit is exacerbated by a reflexive attentional bias toward ipsilesional items. Here we show that, in addition to these spatially lateralized failures, neglect patients also exhibit a severe bias favouring stimuli presented at fixation. We tested neglect patients and matched healthy and right-hemisphere damaged patients without neglect in a task requiring saccade execution to targets in the left or right hemifield. Targets were presented alone or simultaneously with a distracter that appeared in the same hemifield, in the opposite hemifield, or at fixation. We found two fundamental biases in saccade initiation of neglect patients: irrelevant distracters presented in the preserved hemifield tended to capture gaze reflexively, resulting in a large number of saccades erroneously directed toward the distracter. Additionally, distracters presented at fixation severely disrupted saccade initiation irrespective of saccade direction, leading to disproportionately increased latencies of left and right saccades. This latency increase was specific to oculomotor responses of neglect patients and was not observed when a manual response was required. These results show that, in addition to their failure to inhibit reflexive glances toward ipsilesional items neglect patients exhibit a strong oculomotor bias favouring fixated stimuli. We conclude that impaired initiation of saccades in any direction contributes to the deficits of spatial exploration that characterize spatial neglec

Fake or Fantasy: Rapid Dissociation between Strategic Content Monitoring and Reality Filtering in Human Memory

Memory verification is crucial for meaningful behavior. Orbitofrontal damage may impair verification and induce confabulation and inappropriate acts. The strategic retrieval account explains this state by deficient monitoring of memories' precise content, whereas the reality filter hypothesis explains it by a failure of an orbitofrontal mechanism suppressing the interference of memories that do not pertain to reality. The distinctiveness of these mechanisms has recently been questioned. Here, we juxtaposed these 2 mechanisms using high-resolution evoked potentials in healthy subjects who performed 2 runs of a continuous recognition task which contained pictures that precisely matched or only resembled previous pictures. We found behavioral and electrophysiological dissociation: Strategic content monitoring was maximally challenged by stimuli resembling previous ones, whereas reality filtering was maximally challenged by identical stimuli. Evoked potentials dissociated at 200-300 ms: Strategic monitoring induced a strong frontal negativity and a distinct cortical map configuration, which were particularly weakly expressed in reality filtering. Recognition of real repetitions was expressed at 300-400 ms, associated with ventromedial prefrontal activation. Thus, verification of a memory's concordance with the past (its content) dissociates from the verification of its concordance with the present. The role of these memory control mechanisms in the generation of confabulations and disorientation is discusse

Behaviorally spontaneous confabulation in limbic encephalitis: The roles of reality filtering and strategic monitoring

Behaviorally spontaneous confabulation is characterized by a confusion of reality evident in currently inappropriate acts that patients justify with confabulations and in disorientation. Here, we describe a 38-year-old woman lawyer hospitalized because of non-herpetic, presumably autoimmune, limbic encephalitis. For months, she considered herself at work and desperately tried to respect her falsely believed professional obligations. In contrast to a completely erroneous concept of reality, she did not confabulate about her remote personal past. In tasks proposed to test strategic retrieval monitoring, she produced no confabulations. As expected, she failed in tasks of reality filtering, previously shown to have high sensitivity and specificity for behaviorally spontaneous confabulation and disorientation: she failed to suppress the interference of currently irrelevant memories and she had deficient extinction capacity. The observation underscores the special status of behaviorally spontaneous confabulation among confabulatory phenomena and of reality filtering as a thought control mechanism. We suggest that different processes may underlie the generation of false memories and their verbal expression. We also emphasize the need to present theories of confabulation together with experimental tasks that allow one to empirically verify the theories and to explore underlying physiological mechanisms. (JINS, 2010, 16, 995-1005.