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Biomedical subjects

A Schnider

Publications and source records attributed to A Schnider.

At least 19 recordsLinked to original sources
PubMed2003

Perioperative detection of disseminated tumour cells is an independent prognostic factor in patients with colorectal cancer.

BACKGROUND: The objective of the present investigation was to assess the prognostic significance of disseminated tumour cells in peritoneal lavage, and peripheral and mesenteric venous blood in patients undergoing curative resection of colorectal cancer. METHODS: The prognostic impact of perioperative cytological and immunocytochemical detection of disseminated colorectal cancer cells was evaluated prospectively. Peritoneal lavage fluid, and peripheral and mesenteric venous blood from 53 consecutive patients undergoing curative surgery for colorectal cancer were analysed. The dichotomous results (positive versus negative) from the cytological and immunocytochemical analysis were used as a predictor along with other co-variates in proportional hazard regression models of disease-free and overall survival. RESULTS: Disseminated colorectal cancer cells were found in 13 of 53 patients (25 per cent) using cytology (CYT) and/or immunocytochemistry (ICC). The median follow-up at the time of the analysis was 37 months. In multivariate proportional hazard regression models CYT/ICC status was a significant predictor for disease-free (P = 0.002) and overall (P = 0.006) survival. CONCLUSION: Disseminated tumour cells detected by CYT and ICC represent an independent prognostic factor in patients undergoing surgery for colorectal cancer and may identify patients at high risk of recurrence.

Adult↗
PubMed2001

Hypothalamic amnesia with spontaneous confabulations: a clinicopathologic study.

Previous studies demonstrated that patients producing spontaneous confabulations fail to suppress currently irrelevant memory traces and have anterior limbic lesions, particularly involving the orbitofrontal cortex or the basal forebrain. Here, a woman is described who had sarcoidosis damaging the medial hypothalamus and endocrine dysfunction, and a severe memory failure characterized by spontaneous confabulation, disorientation, and severely impaired free recall with preserved recognition. Isolated hypothalamic damage may produce the same type of memory disorder as orbitofrontal damage.

Aged↗
PubMed2001

[Minimal invasive surgery. Aspects of surgical oncology of the gastrointestinal tract].

The general potential and current position of minimally invasive surgery for the surgical treatment of malignant tumours of the gastrointestinal tract are discussed. A reliable validation of these procedures for tumour surgery is still impossible due to the lack of long-term results, the selective experience, and the ongoing process of learning and development. However, it seems clear that minimally invasive procedures will have an important position within surgical oncology. This is especially true with respect to improved staging of gastrointestinal tumours by laparoscopy and various palliative procedures that may be performed laparoscopically. Minimally invasive procedures may suffice for the treatment of certain, highly selected cases of preneoplastic and early cancerous lesions. The definitive acceptance of minimally invasive procedures in the future will require further clinical, preferably randomised trials, comparing the advantages of the minimally invasive access route to possible long-term disadvantages with regard to recurrence-free and overall survival.

Gastrointestinal Neoplasms↗
PubMed2001

Time estimation in Parkinson's disease: normal long duration estimation despite impaired short duration discrimination.

It has been claimed that patients with Parkinson's disease (PD) are deficient in estimating and reproducing time intervals in the range of seconds. This deficit is more severe when subjects are requested to count internally during the demanded intervals, and when the rate of internal counting is fast. The observed deficit might therefore reflect slow internal counting, i. e. motor slowness, rather than a specific deficit of temporal processing. However, PD patients also have a higher temporal discrimination threshold for sensory stimuli, a finding purportedly indicating a slow 'internal clock'. In this study we examined PD patients' processing of short durations (approx. 1s,'psychological present') and long durations (up to 48 s,'extended present'). In the first experiment the ability to discriminate between temporally overlapping presentations of two visual stimuli (darkened rectangles on the computer screen) in the range of one second was tested. In the second experiment PD patients' ability to estimate time intervals between 12 and 48 s was investigated. During these intervals, subjects were required to tap and read a random number on the computer screen at a rate of 1 Hz. We found that the patients were impaired at discriminating between short intervals. This deficit was independent of task difficulty and appeared to be based on an impairment of divided attention. Despite this deficit, the PD patients estimated time intervals up to 48 s as accurately as the controls. We suggest that time estimation, i. e. the feeling for the flow of time, is normal in PD patients despite impaired discrimination of brief intervals in the range of seconds.

Aged↗
PubMed2001

Spontaneous confabulation, reality monitoring, and the limbic system--a review.

Patients with anterior limbic damage may present a distinct syndrome, spontaneous confabulation: they fail in common memory tests, act on the basis of previous habits rather than currently relevant memories, produce confabulations composed of elements of past true events, are disorientated, and are absolutely convinced about the veracity of their perceived reality. Spontaneous confabulation is independent of other false memories, such as, provoked confabulations or illusory recognition. Studies showed that spontaneous confabulators fail to suppress (inactivate) evoked memories that do not pertain to ongoing reality. Rehabilitation differs from other memory failures. Prognosis depends on the lesion site, but recovery is always associated with recovery of this suppression capacity. Lesions typically involve the posterior medial orbitofrontal cortex or its connections in the basal forebrain. Imaging and evoked potential studies in healthy subjects support the idea that the anterior limbic system provides a reality monitoring mechanism which selects memories of current relevance by suppressing (inactivating) currently irrelevant memories. This mechanism appears to adjust the cortical representation of activated memories before their content is recognised and consolidated. Comparison with animal studies suggests that human reality monitoring is a property of the brain's reward system.

Delusions↗
PubMed2001

Prophylactic surgery in families with familial adenomatous polyposis (FAP) and in colitis.

Colorectal cancer is the second most common cause of death from malignant tumors in western countries with approximately 3800 new cases/year in Switzerland. For individuals known to be at high risk for the development of colorectal cancer, screening, chemoprevention and/or prophylactic surgery are the only tools to avoid unnecessary premature death from this disease. With modern molecular and/or genetic testing the risk of developing colorectal cancer can be more precisely estimated on an individualized basis. These individuals need to be enrolled in strong surveillance programs and are clear candidates for prophylactic surgery. The risk of prophylactic surgery (morbidity, mortality, quality of life following surgery) must be clearly weighted against the increasing risk of cancer. These patients should be treated in experienced centers for colorectal surgery in close connection with a genetic testing and counseling team, a molecular laboratory and a psychological support group.

Adenomatous Polyposis Coli↗
PubMed2001

Probabilistic contingency learning with limbic or prefrontal damage.

A fundamental capacity of the human brain is to learn relations (contingencies) between environmental stimuli and the consequences of their occurrence. Some contingencies are probabilistic; that is, they predict an event in some situations but not in all. Animal studies suggest that damage to limbic structures or the prefrontal cortex may disturb probabilistic learning. The authors studied the learning of probabilistic contingencies in amnesic patients with limbic lesions, patients with prefrontal cortex damage, and healthy controls. Across 120 trials, participants learned contingent relations between spatial sequences and a button press. Amnesic patients had learning comparable to that of control subjects but failed to indicate what they had learned. Across the last 60 trials, amnesic patients and control subjects learned to avoid a noncontingent choice better than frontal patients. These results indicate that probabilistic learning does not depend on the brain structures supporting declarative memory.

Adult↗
PubMed2001

Dissociated active and passive tactile shape recognition: a case study of pure tactile apraxia.

Disorders of tactile object recognition (TOR) may result from primary motor or sensory deficits or higher cognitive impairment of tactile shape representations or semantic memory. Studies with healthy participants suggest the existence of exploratory motor procedures directly linked to the extraction of specific properties of objects. A pure deficit of these procedures without concomitant gnostic disorders has never been described in a brain-damaged patient. Here, we present a patient with a right hemispheric infarction who, in spite of intact sensorimotor functions, had impaired TOR with the left hand. Recognition of 2D shapes and objects was severely deficient under the condition of spontaneous exploration. Tactile exploration of shapes was disorganized and exploratory procedures, such as the contour-following strategy, which is necessary to identify the precise shape of an object, were severely disturbed. However, recognition of 2D shapes under manually or verbally guided exploration and the recognition of shapes traced on the skin were intact, indicating a dissociation in shape recognition between active and passive touch. Functional MRI during sensory stimulation of the left hand showed preserved activation of the spared primary sensory cortex in the right hemisphere. We interpret the deficit of our patient as a pure tactile apraxia without tactile agnosia, i.e. a specific inability to use tactile feedback to generate the exploratory procedures necessary for tactile shape recognition.

Adult↗
PubMed2000

Selection of currently relevant memories by the human posterior medial orbitofrontal cortex.

We have demonstrated previously that patients producing spontaneous confabulations fail to suppress currently irrelevant memory traces, so that they act and think on the basis of a false, temporally displaced (past) reality. All spontaneous confabulators had anterior limbic damage, in particular of the orbitofrontal cortex and basal forebrain. These findings indicated that these structures are essential for distinguishing between mental representations of ongoing reality and currently irrelevant memories. In the present study, we used a similar experimental paradigm as in our clinical studies and H(2)(15)O positron emission tomography to explore the selection of currently relevant memories by the healthy human brain. Subjects were repeatedly presented with the same set of pictures, arranged in different order each time, and were requested to indicate picture recurrences within the runs. Thus, performance in the first run depended on new learning, whereas subsequent runs required the distinction between picture repetitions within the current run ("now") and previous picture presentations in earlier runs. Whereas initial learning activated medial temporal structures, subsequent runs provoked circumscribed posterior medial orbitofrontal activation. We suggest that this area is essential for sorting out mental associations that pertain to ongoing reality.

Adult↗
PubMed2000

Recovery from spontaneous confabulations parallels recovery of temporal confusion in memory.

BACKGROUND: In previous studies, the authors found that patients with spontaneous confabulation differ from those with nonconfabulating amnesia by 1) temporal context confusion (TCC) in memory based on an inability to suppress intrusions of currently irrelevant memory traces into ongoing thinking; and 2) lesions involving the orbitofrontal cortex, basal forebrain, or amygdala and perirhinal cortex. OBJECTIVES: To study the long-term clinical course of spontaneous confabulations, determine whether TCC in memory also parallels the clinical course of spontaneous confabulations, and study the impact of lesion site on clinical course. METHODS: Eight patients with spontaneous confabulation were re-examined 18 months after onset. Tests of memory and executive functioning and measurement of TCC in memory were again applied. MRI according to a standard protocol was performed to determine areas of permanent damage. RESULTS: Seven patients eventually stopped confabulating. TCC, but not common memory or executive tests, precisely paralleled the course of spontaneous confabulations. Patients with isolated, less extensive, orbitofrontal lesions stopped confabulating first and had the best neuropsychological outcome. Patients with basal forebrain lesions continued to confabulate for several months and remained amnesic. One patient with extensive orbitofrontal damage and perirhinal cortex damage continues to confabulate after more than 3 years, continuing to confuse memory traces. CONCLUSIONS: Temporal context confusion in memory is not only the sole feature reliably separating patients with spontaneous confabulation from those with nonconfabulating amnesia in the acute stage, it is also the only feature that precisely parallels the clinical course of spontaneous confabulations. Most patients eventually stop confabulating but duration of confabulations depends on the lesion site.

Adult↗
PubMed2000

Spontaneous confabulations, disorientation, and the processing of 'now'.

We have previously demonstrated that spontaneous confabulations and disorientation in amnesia emanate from temporal context confusion in memory characterised by intrusion of previously acquired information into ongoing thinking. This failure appears to be due to an inability to suppress previously activated memory traces of events dating back hours, weeks or even years. In the present study, the possibility was explored that spontaneous confabulators also have a problem in processing information in the very short-term range of the psychological present (the 'now'), which has been defined as the duration of an experiential process. Tasks assessing the processing of time within the psychological present were devised to test this possibility. In experiment 1, spontaneous confabulators, in comparison with other amnestic patients, failed to discriminate brief, visually presented intervals in the now. In experiment 2, they failed to make motion-associated time estimations within the now. These deficits also correlated with disorientation. Although these results do not prove a causal relationship, they indicate that spontaneously confabulating and disorientated patients typically do fail to process information within the 'now'.

Adolescent↗
PubMed1999

Spontaneous confabulators fail to suppress currently irrelevant memory traces.

Human actions require integration of past experiences, ongoing percepts and future concepts. To adapt behavior to reality, the brain must identify mental representations of current relevance. Occasional amnesic subjects act according to invented stories ('spontaneous confabulations'), disregarding present reality. We used repeated runs of a continuous recognition task to measure the ability to distinguish currently relevant from previously encountered but currently irrelevant information. Spontaneous confabulators detected target items as accurately as nonconfabulating amnesics, but increasingly failed to suppress false-positive responses, confusing presentation in previous runs with presentation in the current run. Lesions involved the anterior limbic system: medial orbitofrontal cortex, basal forebrain, amygdala and perirhinal cortex or medial hypothalamus. We suggest that the anterior limbic system represents 'now' in human thinking by suppressing currently irrelevant mental associations.

Amnesia↗
PubMed1998

Association learning in the acute confusional state.

The usefulness of cognitive rehabilitative treatment in the acute stages after brain injury seems questionable because patients in severe acute confusional state early after coma clinically seem unable to learn and store new information. Therefore, the capability of patients in acute confusional state to learn and retain associative information was assessed. On two occasions pairs of simple nouns were presented to six patients in severe acute confusional state. Stimuli were presented repeatedly either in written form only or with additional pictorial representations. Immediate and 20 minutes delayed recall was measured. Patients in acute confusional state were able to learn progressively more word pairs across several presentations. They retained some information over an interval of 20 minutes. In addition, they learned and remembered pictorially supported associations better than pure verbal associations. Patients in severe acute confusional state may retain some explicit information and may profit from an imagery mnemonic aid. These results were not expected on the basis of clinical findings alone and they have potential implications for the care of patients in acute confusional state.

Adult↗
PubMed1997

Ideomotor apraxia: behavioral dimensions and neuroanatomical basis.

Ideomotor apraxia, disordered movement execution to command, commonly follows left-hemisphere damage, implying left-hemisphere dominance for certain kinds of movements. To delineate this dominance we used different command modalities to elicit meaningful movements and tested imitation of nonsense movements. Twenty-seven patients with unilateral hemispheric stroke and 10 age-matched controls were evaluated. Patients with left-hemisphere damage performed both meaningful and nonsense movements poorer than the other study groups; thus, the meaningfulness of the movements is irrelevant for the left-hemisphere motor dominance. The performance varied, however, with the command modality and movement type. Based on this and earlier studies we posit that the left-hemisphere motor dominance is determined by the artificiality of the test situation (it concerns movements performed to command and out of the natural context) and increased spatial and temporal complexity of the demanded movements. No association between the lesion locus within the left hemisphere and the severity of the ideomotor apraxia was found.

Aged↗
PubMed1996

The mechanisms of spontaneous and provoked confabulations.

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 nonexistent 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 together.

Adult↗
PubMed1996

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 20-item 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 memory.

Adult↗
PubMed1996

Memory without context: amnesia with confabulations after infarction of the right capsular genu.

OBJECTIVE: To explore the mechanism of an amnesia marked by confabulations and lack of insight in a patient with an infarct of the right inferior capsular genu. The confabulations could mostly be traced back to earlier events, indicating that the memory disorder ensued from an inability to store the temporal and spatial context of information acquisition rather than a failure to store new information. METHODS: To test the patient's ability to store the context of information acquisition, two experiments were composed in which she was asked to decide when or where she had learned the words from two word lists presented at different points in time or in different rooms. To test her ability to store new information, two continuous recognition tests with novel non-words and nonsense designs were used. Recognition of these stimuli was assumed to be independent of the context of acquisition because the patient could not have an a priori sense of familiarity with them. RESULTS: The patient performed at chance in the experiments probing knowledge of the context of information acquisition, although she recognised the presented words almost as well as the controls. By contrast, her performance was normal in the recognition tests with non-words and nonsense designs. CONCLUSION: These findings indicate that the patient's amnesia was based on an inability to store the context of information acquisition rather than the information itself. Based on an analysis of her lesion, which disconnected the thalamus from the orbitofrontal cortex and the amygdala, and considering the similarities between her disorder, Wernicke-Korsakoff syndrome, and the amnesia after orbitofrontal lesions, it is proposed that contextual amnesia results from interruption of the loop connecting the amygdala, the dorsomedial nucleus, and the orbitofrontal cortex.

Amnesia↗