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Armin Schnider

Publications and source records attributed to Armin Schnider.

At least 19 recordsLinked to original sources
PubMed2006

A technique to train new oculomotor behavior in patients with central macular scotomas during reading related tasks using scanning laser ophthalmoscopy: immediate functional benefits and gains retention.

BACKGROUND: Reading with a central scotoma involves the use of preferred retinal loci (PRLs) that enable both letter resolution and global viewing of word. Spontaneously developed PRLs however often privilege spatial resolution and, as a result, visual span is commonly limited by the position of the scotoma. In this study we designed and performed the pilot trial of a training procedure aimed at modifying oculomotor behavior in subjects with central field loss. We use an additional fixation point which, when combined with the initial PRL, allows the fulfillment of both letter resolution and global viewing of words. METHODS: The training procedure comprises ten training sessions conducted with the scanning laser ophthalmoscope (SLO). Subjects have to read single letters and isolated words varying in length, by combining the use of their initial PRL with the one of an examiner's selected trained retinal locus (TRL). We enrolled five subjects to test for the feasibility of the training technique. They showed stable maculopathy and persisting major reading difficulties despite previous orthoptic rehabilitation. We evaluated ETDRS visual acuity, threshold character size for single letters and isolated words, accuracy for paragraphed text reading and reading strategies before, immediately after SLO training, and three months later. RESULTS: Training the use of multiple PRLs in patients with central field loss is feasible and contributes to adapt oculomotor strategies during reading related tasks. Immediately after SLO training subjects used in combination with their initial PRL the examiner's selected TRL and other newly self-selected PRLs. Training gains were also reflected in ETDRS acuity, threshold character size for words of different lengths and in paragraphed text reading. Interestingly, subjects benefited variously from the training procedure and gains were retained differently as a function of word length. CONCLUSION: We designed a new procedure for training patients with central field loss using scanning laser ophthalmoscopy. Our initial results on the acquisition of newly self-selected PRLs and the development of new oculomotor behaviors suggest that the procedure aiming primarily at developing an examiner's selected TRL might have initiated a more global functional adaptation process.

Aged↗
PubMed2006

Selection of currently relevant words: an auditory verbal memory study using positron emission tomography.

Clinical and imaging studies have shown that the posterior and anterior parts of the limbic system make distinct contributions to memory processing. Whereas the medial temporal lobes and connected structures are important for learning and recognition of new information, the posterior orbitofrontal cortex appears to be crucial for the selection of currently relevant memories, that is, the ability to distinguish between memories that pertain to ongoing reality and memories that do not. Previous studies demonstrating this dissociation used repeated continuous recognition tasks with visual stimuli. In this H2O positron emission tomography study, we demonstrate that this same organizing principle also applies to auditory verbal information, that is, to the processing of auditorily presented words.

Acoustic Stimulation↗
PubMed2006

Computerised treatment of anomia in acute aphasia: treatment intensity and training size.

In this study we analysed the outcome of computer-assisted therapy (CAT) for anomia on eight acute aphasic patients. Since therapy for anomia generally leads to an item-specific effect, the aim of the present study was to investigate whether it is possible to enhance recovery from anomia by increasing the number of treated items. Two periods of five daily written-naming CAT sessions were compared: In one period the CAT included one set of 48 words (single list) and in the other period a double list of 96 items was treated. Seven out of eight patients improved in naming performance for treated items. Overall gains were superior after practising the double list, despite fewer item repetitions. These results suggest that the size of the effect of therapy for anomia depends more on the number of treated items than on the number of repetitions per item. The integration of these results within the framework of studies on intensity is discussed.

Acute Disease↗
PubMed2005

Reality confusion in spontaneous confabulation.

A woman produced spontaneous confabulations after rupture of an anterior communicating artery aneurysm. She confused currently irrelevant with currently relevant information in implicit memory; confabulations about people concerned only new acquaintances; false reality could be induced by an intensive 5-minute discussion; and in a recognition task, she confused false repetitions in another modality with real item repetitions. The findings support the theory that the defect causing spontaneous confabulation precedes conscious memory processing.

Basal Nucleus of Meynert↗
PubMed2005

What does recovery from anomia tell us about the underlying impairment: the case of similar anomic patterns and different recovery.

Although word-finding difficulties have been largely studied from a theoretical and a rehabilitation point of view, recovery mechanisms and especially the fact that patients with similar anomic patterns may exhibit different recovery, are still not fully understood. In the first part of the present study we investigated the word retrieval curve during therapy and the psycholinguistic variables affecting word-finding recovery patterns in three anomic subjects (PG, AH and TM). Despite the fact that all patients had similar anomia at baseline, they presented different recovery patterns during an identical therapy program. The progress during therapy and the number of sessions necessary to reach satisfactory improvement was similar in two patients (AH and TM), but differed in the third patient (PG), who needed more treatment sessions. Moreover, these two different patterns were affected by different psycholinguistic variables: words age of acquisition predicted improvement in AH and TM, whereas phonological neighbourhood predicted improvement in PG. Following the observation that phonological neighbourhood density affected the slower progress during therapy, in the second study we analysed whether this variable also predicts pseudo-word learning in healthy controls and in anomic subjects. Indeed, phonological neighbourhood predicted pseudo-word learning speed in controls and in some anomic patients. We suggest that the analysis of progress during therapy for anomia and the comparison of the variables affecting learning and recovery may provide information about the underlying nature of the anomic deficit that is not available through the simple assessment of performance.

Adult↗
PubMed2005

Effects of baseline task position on apparent activation in functional imaging of memory.

Brain activation dissociates during the repeated performance of memory tasks with decreasing medial temporal and increasing orbitofrontal activation. The impact of such adaptations on a baseline task is unknown. In this study, we used H2(15)O positron emission tomography (PET) in two groups of subjects performing a continuous recognition task and a baseline task. The group performing the baseline task after the main task showed significant medial temporal activation in the subtraction (recognition task-baseline). The group performing the baseline task at the beginning showed right orbitofrontal activation. These differences appeared to result primarily from different activations during the baseline task. It thus appears that the temporal context of a baseline task may fundamentally alter cognitive requirements and substantially influence apparent brain activation during a memory task. We suggest that the automatic filtration of memories according to their relevance for ongoing reality, a capacity mediated by the orbitofrontal cortex, is one such influence on apparent activation.

Adult↗
PubMed2005

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 salience.

Adult↗
PubMed2005

Dynamic modulation of visual detection by auditory cues in spatial neglect.

One of the most constant findings of studies about selective attention is that detection of visual stimuli is enhanced when a visual cue is presented at the position of the upcoming target. In healthy participants, comparable benefits were reported when the cue was presented in a different modality than the target. The aim of this study was to examine spatial and temporal dynamics of visual attention following auditory cues in patients with spatial neglect. Twelve healthy subjects and five patients with left-sided neglect were asked to react to a small vertical line presented randomly at one of four positions. The target appeared 150 or 1000 ms after an auditory cue that was either static (continuous 380 Hz tone presented to the left or right ear) or dynamic (380 Hz tone moving from the left to the right ear or vice versa). The reaction time pattern of healthy participants was unaffected by the different tones. In contrast, reaction times of neglect patients were significantly faster to left targets following a dynamic tone moving from right to left in comparison to a tone moving from left to right. Interestingly, static unilateral tones modulated visual attention of neglect patients to a lesser degree than dynamic tones. The modulation of visual attention by dynamic auditory cues was of short duration and disappeared after 1000 ms. These results demonstrate a fast automatic shift of spatial attention in the direction of a moving tone, suggesting strong dynamic links between visual and auditory attention in patients with a severe spatial deficit.

Acoustic Stimulation↗
PubMed2005

Processing content or location: distinct brain activation in a memory task.

Objects are defined by their content ("what") and by their location ("where"). In the visual system, processing of these two types of information is segregated into distinct anatomical and functional pathways. Using H2 (15)O positron emission tomography to measure cerebral blood flow, we examined the differences in processing of "what" when compared with "where" information in human memory. We found that the detection of deviations from a previously learned image sequence activates distinct brain regions depending on whether the image's content or its location has changed. When deviations of an image's content had to be detected, the left medial temporal lobe (MTL) activation increased. In contrast, detection of deviations from the learned locations of the objects induced increased activation in the right MTL and in the right parietal cortex. These data demonstrate distinct contributions of the left and right MTL to the processing of "what" vs. "where" in memory.

Adult↗
PubMed2005

Functional magnetic resonance imaging and diffusion tensor imaging in a case of central poststroke pain.

The role of the lesion location within functional pain systems is not fully understood for central poststroke pain (CPSP) pathogenesis. In a patient with CPSP we used data from both functional magnetic resonance imaging (MRI) and diffusion tensor imaging (DTI) for anatomo-functional correlations. Structural MRI showed a small residual cavity confined to the right thalamic ventral posterolateral nucleus and the adjacent posterior arm of the internal capsule. DTI maps showed selective reduction of right sensory thalamocortical fibers. Functional MRI, performed with different thermonociceptive stimuli, showed pain-specific signal changes in the anterior cingulate gyrus (BA 24/32) and in the associative parietal regions (BA 5/7). These findings underline, for CPSP pathogenesis, the role of damage of lateral nociceptive thalamoparietal fibers together with the release of activity of anterior cingulate and posterior parietal regions. In a patient with CPSP, we combined noninvasive neuroimaging techniques (functional and diffusion MRI) to assess the anatomo-functional relationship in CPSP. Our investigations show, for CPSP pathogenesis, the role of damage of lateral nociceptive thalamoparietal fibers together with the release of activity of anterior cingulate and posterior parietal regions.

Aged↗
PubMed2005

The human orbitofrontal cortex monitors outcomes even when no reward is at stake.

The orbitofrontal cortex (OFC) processes the occurrence or omission of anticipated rewards, but clinical evidence suggests that it might serve as a generic outcome monitoring system, independent of tangible reward. In this positron emission tomography (PET) study, normal human subjects performed a series of tasks in which they simply had to predict behind which one of two colored rectangles a drawing of an object was hidden. While all tasks involved anticipation in that they had an expectation phase between the subject's prediction and the presentation of the outcome, they varied with regards to the uncertainty of outcome. No comment on the correctness of the prediction, no record of ongoing performance, and no reward, not even a score, was provided. Nonetheless, we found strong activation of the OFC: in comparison with a baseline task, the left anterior medial OFC showed activation in all conditions, indicating a basic role in anticipation; the left posterior OFC was activated in all tasks with some uncertainty of outcome, suggesting a role in the monitoring of outcomes; the right medial OFC showed activation exclusively during guessing. The data indicate a generic role of the human OFC, with some topical specificity, in the generation of hypotheses and processing of outcomes, independent of the presence of explicit reward.

Frontal Lobe↗
PubMed2004

Mechanism of disorientation in Alzheimer's disease.

In nondemented amnesics, disorientation mostly reflects a failure to select memories that pertain to ongoing reality (increased temporal context confusion; TCC), a failure strongly associated with orbitofrontal damage. In the present study, we used the same paradigm--2 runs of a continuous recognition task--in 23 patients with mild to moderate Alzheimer's disease (AD) (Clinical Dementia Rating Scale score of 1-2). We found that disorientation was frequent in this sample (52%). However, although it correlated moderately well with general measures of dementia severity, verbal episodic memory and executive functioning, there was no significant correlation with TCC. Thus, disorientation in AD appears to reflect general cognitive decline rather than a specific cognitive failure such as increased TCC. This finding is compatible with the different distribution of degeneration in AD and the orbitofrontal damage typically present in severely disoriented amnesics.

Aged↗
PubMed2004

Defective spatial imagery with pure Gerstmann's syndrome.

Gerstmann's syndrome comprises finger agnosia, peripheral agraphia, anarithmetia, and right-left confusion. We here report a single-case study of an 85-year-old ambidextrous man who exhibited pure Gerstmann's syndrome (i.e., without aphasia) 10 weeks after a stroke involving the angular gyrus in the left parietal lobe. We hypothesize that, in this case, the main cognitive denominator of Gerstmann's tetrad was a severe dysfunction in mental rotation and translation. This report provides further evidence for the spatial nature of Gerstmann's syndrome.

Aged↗
PubMed2004

Dopamine inhibition and the adaptation of behavior to ongoing reality.

Spontaneous confabulation is a rare memory disorder resulting from orbitofrontal damage or disconnection. Patients act on the basis of memories that do not pertain to the current situation, and are disoriented. No medical treatment is known. Recent studies suggest that subcortical dopaminergic structures are involved in the selection of currently relevant memories. We present a patient who regained the ability to adapt thought and behavior to ongoing reality when treated with risperidone, a dopamine antagonist.

Adaptation, Physiological↗
PubMed2004

Rapid discrimination of visual and multisensory memories revealed by electrical neuroimaging.

Though commonly held that multisensory experiences enrich our memories and that memories influence ongoing sensory processes, their neural mechanisms remain unresolved. Here, electrical neuroimaging shows that auditory-visual multisensory experiences alter subsequent processing of unisensory visual stimuli during the same block of trials at early stages poststimulus onset and within visual object recognition areas. We show this with a stepwise analysis of scalp-recorded event-related potentials (ERPs) that statistically tested (1) ERP morphology and amplitude, (2) global electric field power, (3) topographic stability of and changes in the electric field configuration, and (4) intracranial distributed linear source estimations. Subjects performed a continuous recognition task, discriminating repeated vs. initial image presentations. Corresponding, but task-irrelevant, sounds accompanied half of the initial presentations during a given block of trials. On repeated presentations within a block of trials, only images appeared, yielding two situations-the image's prior presentation was only visual or with a sound. Image repetitions that had been accompanied by sounds yielded improved memory performance accuracy (old or new discrimination) and were differentiated as early as approximately 60-136 ms from images that had not been accompanied by sounds through generator changes in areas of the right lateral-occipital complex (LOC). It thus appears that unisensory percepts trigger multisensory representations associated with them. The collective data support the hypothesis that perceptual or memory traces for multisensory auditory-visual events involve a distinct cortical network that is rapidly activated by subsequent repetition of just the unisensory visual component.

Adolescent↗
PubMed2004

Receptive amusia: temporal auditory processing deficit in a professional musician following a left temporo-parietal lesion.

This study examined the musical processing in a professional musician who suffered from amusia after a left temporo-parietal stroke. The patient showed preserved metric judgement and normal performance in all aspects of melodic processing. By contrast, he lost the ability to discriminate or reproduce rhythms. Arrhythmia was only observed in the auditory modality: discrimination of auditorily presented rhythms was severely impaired, whereas performance was normal in the visual modality. Moreover, a length effect was observed in discrimination of rhythm, while this was not the case for melody discrimination. The arrhythmia could not be explained by low-level auditory processing impairments such as interval and length discrimination and the impairment was limited to auditory input, since the patient produced correct rhythmic patterns from a musical score. Since rhythm processing was selectively disturbed in the auditory modality, the arrhythmia cannot be attributed to a impairment of supra-modal temporal processing. Rather, our findings suggest modality-specific encoding of musical temporal information. Besides, it is proposed that the processing of auditory rhythmic sequences involves a specific left hemispheric temporal buffer.

Acoustic Stimulation↗
PubMed2004

Disorganised memory after right dorsolateral prefrontal damage.

Neurophysiological and functional brain imaging studies suggest the importance of dorsolateral area 9/46 for modality-independent working memory. However, the behavioural manifestations following isolated damage to this area have not been clearly outlined. Here, we describe the dramatic derangement of pragmatic memory after circumscribed lesion of the right area 9/46. A 52 year-old woman had suffered a traumatic brain injury 13 years ago and sought help for what she thought was a severe memory disorder. She regularly missed appointments and had gradually lost all her friends. She had tried different strategies to compensate for her memory problem, such as writing notes on her wrist or using electronic organizers. Intelligence, attention, verbal long-term memory, and executive functions were normal. Furthermore, experimental exploration demonstrated intact time estimation, attribution of memories to ongoing reality, and anticipation of outcomes. However, she failed to rehearse and manipulate information in working memory (n-back task), confirming the findings of functional imaging studies that the mid-dorsolateral prefrontal cortex is involved in mental manipulation of information. This case exemplifies that an isolated lesion of the right area 9/46 may induce severe failure to schedule actions and memory retrieval, a disorder leading to severely disorganised behaviour and disability.

Brain Injuries↗