Rehabilitation of hemianopia and visuospatial hemineglect with a mixed intervention including adapted boxing therapy: An exploratory case study.

Visual field loss and visuospatial neglect are frequent consequences of cerebral stroke. They often have a strong impact on independence in many daily activities. Rehabilitation aiming to decrease these disabilities is therefore important, and several techniques have been proposed to foster awareness, compensation, or restitution of the impaired visual field. We here describe a rehabilitation intervention using adapted boxing therapy that was part of a pluridisciplinary intervention tailored for a particular case. A 58-year-old man with left homonymous hemianopia (HH) and mild visuospatial hemineglect participated in 36 sessions of boxing therapy six months after a right temporo-occipital stroke. Repeated stimulation of his blind and neglected hemifield, and training to compensate for his deficits through improved use of his healthy hemifield were performed through boxing exercises. The patient showed a stable HH before the beginning of the training. After six months of boxing therapy, he reported improved awareness of his visual environment. Critically, his HH had evolved to a left superior quadrantanopia and spatial attention for left-sided stimuli had improved. Several cognitive functions and his mood also showed improvement. We conclude that boxing therapy has the potential to improve the compensation of visuospatial impairments in individual patients with visual field loss.

Absence of an early hippocampal encoding signal after medial temporal lesions: No consequence for the spacing effect.

Immediately repeated meaningful pictures in a continuous recognition task induce a positive frontal potential at about 200-300 ms, which appears to emanate from the medial temporal lobe (MTL) centered on the hippocampus, as concluded from inverse solutions, coherence measurements, and depth electrode recordings in humans. In this study, we tested patients with unilateral MTL lesions due to stroke to verify the provenance of this signal and its association with the spacing effect (SE)-the improved learning of material encountered in spaced rather than massed presentation. We found that unilateral left or right MTL lesions abolished the early frontal MTL-mediated signal but not the spacing effect. We conclude that the SE does not depend on MTL integrity. We suggest that the early frontal signal at 200-300 ms after immediate picture repetition may serve as a direct biomarker of MTL integrity that may be useful in the early stages of diseases like Alzheimer's.

Rapid memory stabilization by transient theta coherence in the human medial temporal lobe.

Presenting stimuli again after presentation of intervening stimuli improves their retention, an effect known as the spacing effect. However, using event-related potentials (ERPs), we had observed that immediate, in comparison to spaced, repetition of pictures induced a positive frontal potential at 200-300 ms. This potential appeared to emanate from the left medial temporal lobe (MTL), a structure critical for memory consolidation. In this study, we tested the behavioral relevance of this signal and explored functional connectivity changes during picture repetition. We obtained high-density electroencephalographic recordings from 14 healthy subjects performing a continuous recognition task where pictures were either repeated immediately or after 9 intervening items. Conventional ERP analysis replicated the positive frontal potential emanating from the left MTL at 250-350 ms in response to immediately repeated stimuli. Connectivity analysis showed that this ERP was associated with increased coherence in the MTL region--left more that right--in the theta-band (3.5-7 Hz) 200-400 ms following immediate, but not spaced, repetition. This increase was stronger in subjects who better recognized immediately repeated stimuli after 30 min. These findings indicate that transient theta-band synchronization between the MTL and the rest of the brain at 200-400 ms reflects a memory stabilizing signal.

An electrophysiological dissociation between orbitofrontal reality filtering and context source monitoring.

Memory influences behavior in multiple ways. One important aspect is to remember in what precise context in the past a piece of information was acquired (context source monitoring). Another important aspect is to sense whether an upcoming thought, composed of fragments of memories, refers to present reality and can be acted upon (orbitofrontal reality filtering). Whether these memory control processes share common underlying mechanisms is unknown. Failures of both have been held accountable for false memories, including confabulation. Electrophysiological and imaging studies suggest a dissociation but used very different paradigms. In this study, we juxtaposed the requirements of context source monitoring and reality filtering within a unique continuous recognition task, which healthy participants performed while high-resolution evoked potentials were recorded. The mechanisms dissociated both behaviorally and electrophysiologically: Reality filtering induced a frontal positivity, absence of a specific electrocortical configuration, and posterior medial orbitofrontal activity at 200-300 msec. Context source monitoring had no electrophysiological expression in this early period. It was slower and less accurate than reality filtering and induced a prolonged positive potential over frontal leads starting at 400 msec. The study demonstrates a hitherto unrecognized separation between orbitofrontal reality filtering and source monitoring. Whereas deficient orbitofrontal reality filtering is associated with reality confusion in thinking, the behavioral correlates of deficient source monitoring should be verified with controlled experimental exploration.

Neural Correlate of Anterograde Amnesia in Wernicke-Korsakoff Syndrome.

The neural correlate of anterograde amnesia in Wernicke-Korsakoff syndrome (WKS) is still debated. While the capacity to learn new information has been associated with integrity of the medial temporal lobe (MTL), previous studies indicated that the WKS is associated with diencephalic lesions, mainly in the mammillary bodies and anterior or dorsomedial thalamic nuclei. The present study tested the hypothesis that amnesia in WKS is associated with a disrupted neural circuit between diencephalic and hippocampal structures. High-density evoked potentials were recorded in four severely amnesic patients with chronic WKS, in five patients with chronic alcoholism without WKS, and in ten age matched controls. Participants performed a continuous recognition task of pictures previously shown to induce a left medial temporal lobe dependent positive potential between 250 and 350 ms. In addition, the integrity of the fornix was assessed using diffusion tensor imaging (DTI). WKS, but not alcoholic patients without WKS, showed absence of the early, left MTL dependent positive potential following immediate picture repetitions. DTI indicated disruption of the fornix, which connects diencephalic and hippocampal structures. The findings support an interpretation of anterograde amnesia in WKS as a consequence of a disconnection between diencephalic and MTL structures with deficient contribution of the MTL to rapid consolidation.

Isolated prospective confabulation in Wernicke-Korsakoff syndrome: a case for reality filtering.

A 57-year-old man suffered severe amnesia and disorientation, accompanied by content-specific confabulation, due to an alcoholic Wernicke-Korsakoff syndrome. For months, he was deeply concerned about a single obligation that he thought he had to respond to, but which he had already assumed 20 years previously. This monothematic, prospective confabulation was associated with failures of reality filtering as previously documented in behaviorally spontaneous confabulation and disorientation: the patient failed to suppress the interference of currently irrelevant memories and to abandon anticipations that were no longer valid (impaired extinction capacity). Magnetic resonance imaging showed damage to the mamillary bodies and the dorsomedial thalamic nucleus. Positron emission tomography (FDG-PET) showed extended orbitofrontal hypometabolism. We suggest that isolated prospective confabulation shares the core feature (acts and thoughts based on currently irrelevant memory), mechanism (failure of reality filtering), and anatomical basis (orbitofrontal dysfunction) with behaviorally spontaneous confabulations.

The behavioral significance of coherent resting-state oscillations after stroke.

Stroke lesions induce not only loss of local neural function, but disruptions in spatially distributed areas. However, it is unknown whether they affect the synchrony of electrical oscillations in neural networks and if changes in network coherence are associated with neurological deficits. This study assessed these questions in a population of patients with subacute, unilateral, ischemic stroke. Spontaneous cortical oscillations were reconstructed from high-resolution electroencephalograms (EEG) with adaptive spatial filters. Maps of functional connectivity (FC) between brain areas were created and correlated with patient performance in motor and cognitive scores. In comparison to age matched healthy controls, stroke patients showed a selective disruption of FC in the alpha frequency range. The spatial distribution of alpha band FC reflected the pattern of motor and cognitive deficits of the individual patient: network nodes that participate normally in the affected functions showed local decreases in FC with the rest of the brain. Interregional FC in the alpha band, but not in delta, theta, or beta frequencies, was highly correlated with motor and cognitive performance. In contrast, FC between contralesional areas and the rest of the brain was negatively associated with patient performance. Alpha oscillation synchrony at rest is a unique and specific marker of network function and linearly associated with behavioral performance. Maps of alpha synchrony computed from a single resting-state EEG recording provide a robust and convenient window into the functionality and organization of cortical networks with numerous potential applications.

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 discussed.

Rapid consolidation and the human hippocampus: intracranial recordings confirm surface EEG.

Diverse studies demonstrated that although immediately repeated stimuli are better and faster recognized than stimuli repeated after a delay, this comes at the price of less-efficient long-term retention. A recent-evoked potential study using source estimation of high-resolution scalp EEG indicated that while immediate repetition induced a strikingly different electrical activity than new items in the left-medial temporal lobe (MTL) after 200-300 ms, delayed repetition did not. In this study, we recorded evoked potentials in two epileptic patients with intracranial depth electrodes in diverse temporal and frontal areas as they performed the same task as in the previous study. We found that immediate repetition induced increase of neural activity specifically in the left MTL between 250 and 400 ms compared to new items and items repeated after a delay. The findings are important in two ways. First, they support our previous conclusion that novel information immediately initiates a consolidation process involving the left-hippocampal area, which remains vulnerable during active maintenance and increases its effectiveness during off-line processing. Second, they indicate that source estimation based on high-resolution scalp EEG correctly localizes the current source of electrical activity in midline structures like the MTL.

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.

Abnormal cortical network activation in human amnesia: A high-resolution evoked potential study.

Little is known about how human amnesia affects the activation of cortical networks during memory processing. In this study, we recorded high-density evoked potentials in 12 healthy control subjects and 11 amnesic patients with various types of brain damage affecting the medial temporal lobes, diencephalic structures, or both. Subjects performed a continuous recognition task composed of meaningful designs. Using whole-scalp spatiotemporal mapping techniques, we found that, during the first 200 ms following picture presentation, map configuration of amnesics and controls were indistinguishable. Beyond this period, processing significantly differed. Between 200 and 350 ms, amnesic patients expressed different topographical maps than controls in response to new and repeated pictures. From 350 to 550 ms, healthy subjects showed modulation of the same maps in response to new and repeated items. In amnesics, by contrast, presentation of repeated items induced different maps, indicating distinct cortical processing of new and old information. The study indicates that cortical mechanisms underlying memory formation and re-activation in amnesia fundamentally differ from normal memory processing.

Instinctive modulation of cognitive behavior: a human evoked potential study.

Successful adaptive behavior requires fast information processing. Behavioral switches may be necessary in response to threatening stimuli or when anticipated outcomes fail to occur. In this study, we explored the cortical processing of these two components using high-resolution evoked potentials. Subjects made a reversal learning task where they had to predict which one of two faces had a target stimulus on the nose. We found early electrocortical differences at 100-200 ms depending on whether the target stimulus was a spider or a disk. Source estimation indicated that this distinction was mediated by an anterior medial temporal region including the amygdala and adjacent cortex. When a switch to the alternate face was required, there was a discrete early electrocortical correlate after 200 ms, mediated by ventromedial prefrontal areas. Continued validity of stimulus-target associations was signaled at 400-520 ms, mediated by the parahippocampal region. The study indicates rapid serial processing of innate emotional quality, then cognitive-behavioral relevance of stimuli, mediated by limbic and paralimbic structures.