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Biomedical subjects

R M Klein

Publications and source records attributed to R M Klein.

At least 37 records · Page 2Linked to original sources
PubMed2001

Modulation of the attentional blink by differential resource allocation.

When one masked target (T2) follows another (T1) in close temporal proximity, identification accuracy of the second target is reduced for a period referred to as the attentional blink. Analysis of the attentional blink literature suggests that increasing the difficulty of T1 processing increases the magnitude of the blink. In a previous study that eliminated several untoward features of the typical attentional blink design (e.g., task switching, location switching, and stream contribution), we found no effect on blink magnitude when three levels of T1 difficulty (manipulated in a data-limited manner) were randomly intermixed. Here, when we repeated the previous study using a blocked manipulation of T1 difficulty, which is characteristic of the literature, a significant positive relation between T1 difficulty and blink magnitude was found. Resource allocation put in place to encode T1 in advance of a dual-target trial thus seems to be the critical factor in mediating this relation.

Attention↗
PubMed2001

The attentional blink is immune to masking-induced data limits.

The attentional blink is the robust finding that processing a masked item (T1) hinders the subsequent identification of a backwards masked second item (T2), which follows soon after the first one. There has been some debate about the theoretically important relation between the difficulty of T1 processing and the ensuing blink. In Experiment 1 we manipulated the difficulty of T1 in such a way as to affect the quality of data without altering the amount of resources allocated to its identification. We found no relation between the accuracy of T1 identification and the blink. In Experiment 2, the same difficulty manipulation was applied to T2, and we observed an additive pattern with the blink. Together, this pattern of results indicates that a data-limited difficulty manipulation does not affect the blink, whether applied to T1 or T2. In Experiment 3 we used an individual differences methodology to show that performance in the traditional "stream"-like presentation (rapid serial visual presentation) was highly correlated with performance in our modified "target mask, target mask" paradigm, thus allowing for comparisons beyond the present methodology to much of the previous literature that has used the stream paradigm.

Adult↗
PubMed2001

Visual prior entry.

It has long been claimed that attended stimuli are perceived prior to unattended stimuli--doctrine of prior entry. Most, if not all, studies on which such claims have been based, however, are open to a nonattentional interpretation involving response bias, leading some researchers to assert that prior entry may not exist. Given this controversy, we introduce a novel methodology to minimize the effect of response bias by manipulating attention and response demands in orthogonal dimensions. Attention was oriented to the left or right (ie., spatially), but instead of reporting on the basis of location, observers reported the order (first or second) of vertical versus horizontal line segments. Although second-order response biases were demonstrated, effects of attention in accordance with the law of prior entry were clearly obtained following both exogenous and endogenous attentional cuing.

Adult↗
PubMed2001

Atrial natriuretic peptide-like immunoreactivity in neurons and astrocytes of human cerebellum and inferior olivary complex.

Atrial natriuretic peptide (ANP) has previously been localized in areas of mammalian brain associated with olfaction, cardiovascular function, and fluid/electrolyte homeostasis. Despite the presence of several types of natriuretic peptide receptors in mammalian cerebellum, neither intrinsic nor extrinsic sources of the natriuretic peptides have been described. In this report we describe the immunohistochemical localization of both intrinsic and extrinsic sources for ANP in human cerebellum. ANP-like immunoreactivity (ANP-LIR) was observed in climbing fibers in the cerebellar molecular layer that probably originated from isolated immunopositive neurons of the inferior olivary complex. Intrinsic sources of ANP-LIR included small subpopulations of protoplasmic and fibrous astrocytes and Bergmann glia, as well as Golgi and Lugaro neurons of the granule cell layer. These results suggest that, in addition to its presumptive roles in local vasoregulation, ANP may serve as a modulator of the activity of Purkinje neurons.

Astrocytes↗
PubMed2001

Estrogen and tamoxifen interplay with T(3) in male rats: pharmacologically distinct classes of estrogen responses affecting growth, bone, and lipid metabolism, and their relation to serum GH and IGF-I.

Estrogen (E) and T(3) regulate gene expression by receptor mechanisms that may enable hormonal interplay affecting growth and metabolism. Prior studies of E and tamoxifen (TM) interplay with T(3) in female rats identified a subset of E responses that required T(3) for expression and exhibited large agonist responses to TM. In contrast, TM acted more like an antagonist in most T(3)-independent E responses. This study used male rats to further explore the role of T(3) in E effects on growth and metabolism, and the relation of such effects to changes in serum GH and IGF-I. Orchidectomized, hypothyroid rats were treated 6 wk with vehicle, E2 benzoate (E2B), or TM with or without T(3). The following parameters were measured: body weight change; tibia length and bone mineral density; heart and kidney weight; food intake and body temperature; serum levels of glucose, cholesterol, triglycerides, GH, and IGF-I; seminal vesicle weight; and anterior pituitary levels of GH, PRL, glandular kallikrein, and total protein. Interplay with T(3) contributed to multiple E effects on growth and metabolism, and some E responses involved both T(3)-dependent and T(3)-independent components. Both E2B and TM increased serum GH, but the increases were poorly coupled to IGF-I. Correlation/regression analysis of individual rat data sets suggested distinct roles for GH and IGF-I in specific E effects. E2B and TM effects on somatic growth exhibited positive correlations with IGF-I and negative correlations with GH; effects on bone mineral density and triglycerides exhibited positive correlations with GH and negative correlations with IGF-I. Three pharmacologically distinct classes of in vivo E responses were identified in this study, and TM displayed a profile of biological activity that may be useful for men undergoing androgen-deprivation therapy.

Animals↗
PubMed2001

The presence of a nonresponding effector increases inhibition of return.

Inhibition of return (IOR) refers to the performance disadvantage for targets presented at an exogenously cued location, relative to an uncued location, at relatively long cue-target onset asynchronies. In this experiment, we investigated the influence on IOR of a nonresponding effector (i.e., the index finger of the nonresponding hand) placed on a response key in a simple-RT task. With peripheral cues and targets, IOR and spatial stimulus-response compatibility effects were larger when the nonresponding hand was placed on a response key. IOR--the slowed responding to go signals at the cued location--was accompanied by a lower false alarm rate when no-go signals were presented there. These findings provide direct evidence for a motoric component to IOR wherein some portion of the inhibition is observed as a criterion shift against responding to the cued location.

Adult↗
PubMed2001

Of mice and men: virtual Hebb-Williams mazes permit comparison of spatial learning across species.

We developed a computer-generated virtual environment to test humans, for the first time, on the Hebb-Williams mazes. The goal was to provide a standardized test that could be used to directly compare human performance with that of C57BL/6J mice performing in real versions of the mazes. Such a comparison seems crucial if conclusions regarding genetic manipulations of rodents are to be mapped onto human cognitive disorders. The learning curves across species were strikingly similar, lending support to the rodent model of human spatial memory. Humans learned faster than rodents in both the acquisition and the test portions of the protocol, and females of both species were less efficient in solving these problems than males. These results represent the first modern comparison of human and rodent learning that uses the same test of spatial problem solving.

Adult↗
PubMed2001

Combined expectancies: event-related potentials reveal the early benefits of spatial attention that are obscured by reaction time measures.

Visual spatial attention has been likened to a "spotlight" that selectively facilitates the perceptual processing of events at covertly attended locations. However, if participants have advance knowledge of the likely location of an impending target and the likely response it will require, facilitation in response performance does not occur for targets at the expected (or attended) location that require an unexpected response. Event-related potentials (ERPs) were recorded during a discrimination task in which the most likely target location and target response were simultaneously cued prior to target onset. The ERPs showed evidence of enhanced perceptual-level processing for all targets at attended locations. These results suggest that the lack of response facilitation for unexpected targets at attended locations is likely due to postperceptual processes that are activated by the inclusion of nonspatial stimulus expectancies, response expectancies, or both.

Adult↗
PubMed2000

Early and specific expression of monocyte chemoattractant protein-1 in the thalamus induced by cortical injury.

For many years it has been known that retrograde degeneration of thalamic neurons occurs following damage to the cerebral cortex, however, the molecular mechanisms which control this process are unknown. Recent studies have demonstrated microglial activation in thalamic nuclei well before the onset of retrograde neuronal cell death. Activated monocytes and microglia synthesize factors detrimental to neuronal survival as well as phagocytose damaged and dying neurons. Our previous studies demonstrated that monocyte chemoattractant protein-1 (MCP-1), a beta chemokine which attracts cells of monocytic origin to sites of injury, is rapidly expressed in the brain following visual cortical lesions. The present study examined the expression of MCP-1 messenger RNA and protein in the thalamus following a visual cortical lesion. Aspiration lesions of visual cortex were made in adult mice. At specific times after lesion, brains were harvested and dissected into specific regions. MCP-1 message as detected using northern analysis was absent in uninjured brain, but was elevated in the ipsilateral thalamus as rapidly as 1 h following the lesion. In situ hybridization localized MCP-1 message to subpial glial cells of the lateral geniculate nucleus (LGN) of the ipsilateral thalamus after injury. ELISA showed that MCP-1 protein levels were significantly elevated in the ipsilateral thalamus at 6 h, peaked at 12 h, and remained above baseline levels for at least 1 week post lesion. In addition, anti-GFAP staining demonstrated activated astrocytes localized to the ipsilateral LGN at 24 and 72 h after injury. The early expression and regional localization of MCP-1 mRNA and protein strongly suggest that MCP-1 is a critical molecule in the regulation of thalamic retrograde neuronal degeneration.

Animals↗
PubMed2000

Visual and motor effects in inhibition of return.

Inhibition of return (IOR) refers to slowed reaction times (RTs) when a target appears in the same rather than a different location as a preceding stimulus. The present study tested the hypothesis that IOR reflects a motor bias rather than a perceptual deficit. Two signals (S1 and S2) were presented on each trial. These signals were peripheral onsets or central arrows. The responses required to S1 and S2 were, respectively, no response-manual, manual-manual, saccadic-manual, no response-saccadic, manual-saccadic, and saccadic-saccadic. Uniting perceptual and motor bias views of IOR, the results demonstrated inhibition for responding to (a) peripheral signals when the eyes remained fixed (slowed visual processing) and (b) both peripheral and central signals when the eyes moved (slowed motor production). However, the results also emphasized that the nature of IOR depends fundamentally on the response modality used to reveal its influence.

Adult↗
PubMed2000

The effects of scene inversion on change blindness.

In two experiments, participants searched for a difference between two views of a scene. In Experiment 1, the authors extended the change-blindness findings from previous work by R. A. Rensink, J. K. O'Regan, and J. J. Clark (1997), which used an experimenter-induced global transient, to a less artificial situation in which participants searched for a difference in a pair of photographic images presented simultaneously. To examine the idea that meaning-driven endogenous orienting was responsible for the previously observed advantage for changes in center-of-interest items, the authors inverted half of the image pairs. The advantage for center-of-interest items was replicated with upright displays, but it was completely eliminated by inversion, strongly supporting the role of meaning-driven endogenous orienting in this task. With flickering displays (Experiment 2), the center-of-interest effect was completely unaffected by inversion. The authors suggest that when change blindness is induced via flicker, scene modifications are typically found by stimulus-driven rather than by meaning-driven processes.

Environment↗
PubMed2000

On the manifestations of memory in visual search.

Evidence is presented supporting the thesis that performance in visual search tasks is affected by the contribution of memory processes. Three levels of analysis, corresponding to the various time scales present in a typical search experiment, are discussed. Perceptual learning involves the task and stimulus specific improvement seen across blocks of training. Trial-to-trial priming has an influence which extends over 5-8 trials and lasts on the order of 30 s. Within-trial tagging prevents the re-inspection of already attended (or fixated) items. Also at the within-trial level of analysis, parallel accumulation of evidence for target presence/absence or target location inherently involves memory mechanisms. Organizing the various phenomena in this way makes it apparent that the various mechanisms may interact in a causal way. Within-trial tagging may contribute to priming which may contribute to perceptual learning. Recent proposals that visual search is memoryless (amnesic) are discussed and dismissed.

Awareness↗
PubMed2000

[Inflammation of the myocardium as an arrhythmia trigger].

In patients with acute or chronic myocarditis, arrhythmias are a common and often the only clinical symptom in the natural course of the disease. The potentially malignant tachy- and bradyarrhythmias are of particular significance in the differential diagnosis of sudden cardiac death in myocarditis. Factors responsible for the increased incidence of cardiac arrhythmias are structural changes, parameters of ventricular dynamics and vascular changes. On the one hand, inflammatory processes in the cardiac myocytes and interstitium can lead directly to fluctuations in membrane potential. Fibrosis and scarring of the myocardial tissue and secondary hypertrophy and atrophy of the myocytes favor the development of ectopic pacemakers, late potentials and reentry as a result of inhomogeneous stimulus conduction. Furthermore, parameters of ventricular dynamics such as increased wall tension, increased myocardial oxygen consumption and diminished coronary reserve in the case of disturbed systolic or diastolic left ventricular function also contribute to the increased incidence of arrhythmias. Lastly, vascular factors can further increase the arrhythmogenicity of the inflamed myocardium through the disturbance of micro- and macrovascular perfusion and the resulting myocardial ischemia. Non-invasive rhythmological evaluation by 24 h Holter ECG, measurement of ventricular late potentials and heart rate variability can be used for orienting risk stratification of the at-risk patient with myocarditis. Programmed atrial and ventricular electrophysiological stimulation also has a relatively high predictive value for spontaneous ventricular tachyarrhythmias. It should be emphasized that, at the present time, optimal electrophysiological parameters with a high predictive value do not exist. In a selected patient population, immunosuppressive therapy in addition to conventional antiarrhythmic therapy can lead to the reduction or complete suppression of spontaneous and inducible arrhythmias. Nevertheless, in the interim, further precautionary antiarrhythmic measures such as serial antiarrhythmic treatment, VT ablation and ACID implantation are necessary in patients with malignant cardiac arrhythmias. Right ventricular myocardial biopsy for demonstration or exclusion of myocarditis is an important additional examination which can improve the differential diagnosis and treatment of patients with cardiac arrhythmias of unclear etiology.

Adult↗
PubMed1999

[Clinical course and complications of meningococcal septicemia].

BACKGROUND: Meningococcal septicemia is still associated with high mortality with most deaths occurring within the first 24 hours. CASE REPORT: We report on 3 patients with severe meningiococcemia. All patients had an aprupt onset of clinical illness with fever and unspecific prodomi like arthralgias, myalgias and abdominal pain. On admission all patients had severe prostration, hypotension and tachycardia. Two patients presented purpuric rash and petechiae, meningitis was found in only 1 patient. Gram-negative diplococci were demonstrated in spinal fluid primarily in 2 patients, in all patients meningococcae could be cultured in serial blood specimens. Because of severe cardiorespiratory distress all patients required mechanical ventilation and catecholamine support within 24 hours of diagnosis. Complications of meningococcemia demonstrated by these patients were coagulopathy, meningitis, myocarditis with alterations of echocardiographic and ECG records and elevations of CK levels and surgical relevant peripheral gangrene. Antibiotic therapy was initiated with penicillin on the day of admission, which resulted in stabilisation and recuperation in all patients. CONCLUSIONS: In patients with aprupt onset of acute illness, which include fever and sudden petechial rash, severe meningococcal septicemia has to be taken in consideration without clinical signs of meningitis. The prompt diagnosis, the use of parenteral antiobiotics in suspected meningococcal disease as well as the management of meningococcemia and its complications in intensive care units is crucial for the prognosis of the individual patient.

Adult↗
PubMed1999

Role of primate superior colliculus in preparation and execution of anti-saccades and pro-saccades.

We investigated how the brain switches between the preparation of a movement where a stimulus is the target of the movement, and a movement where a stimulus serves as a landmark for an instructed movement elsewhere. Monkeys were trained on a pro-/anti-saccade paradigm in which they either had to generate a pro-saccade toward a visual stimulus or an anti-saccade away from the stimulus to its mirror position, depending on the color of an initial fixation point. Neural activity was recorded in the superior colliculus (SC), a structure that is known to be involved in the generation of fast saccades, to determine whether it was also involved in the generation of anti-saccades. On anti-saccade trials, fixation during the instruction period was associated with an increased activity of collicular fixation-related neurons and a decreased activity of saccade-related neurons. Stimulus-related and saccade-related activity was reduced on anti-saccade trials. Our results demonstrate that the anti-saccade task involves (and may require) the attenuation of preparatory and stimulus-related activity in the SC to avoid unwanted pro-saccades. Because the attenuated pre-saccade activity that we found in the SC may be insufficient by itself to elicit correct anti-saccades, additional movement signals from other brain areas are presumably required.

Animals↗
PubMed1999

Endogenous plasma endothelin concentrations and coronary circulation in patients with mild dilated cardiomyopathy.

OBJECTIVE: To determine whether increased plasma concentrations of endothelin-1 (ET-1) and big endothelin (BET) play a role in the regulation of coronary circulation in patients with idiopathic dilated cardiomyopathy (IDCM). SETTING: Tertiary referral centre for cardiac diseases. PATIENTS: Fourteen patients (eight male/six female; mean (SD) age 59 (9) years) with IDCM (ejection fraction 36 (9)%) and five normotensive subjects (two male/three female; age 52 (7) years) serving as controls were studied. METHODS: Functional status was classified according to New York Heart Association (NYHA) class. Endogenous ET-1 and BET plasma concentrations from the aorta and the coronary sinus were determined by radioimmunoassay. Coronary blood flow, using the inert chromatographic argon method, myocardial oxygen consumption, and coronary sinus oxygen content under basal conditions were determined. RESULTS: In the aorta, mean (SD) concentrations of ET-1 (IDCM 0.76 (0.25) v controls 0.31 (0.06) fmol/ml; p = 0.002) and BET (IDCM 3.58 (1.06) v controls 2.11 (0.58) fmol/ml; p = 0.014) were increased in patients with IDCM. Aortic ET-1 concentrations correlated positively with NYHA class (r = 0. 731; p < 0.001), myocardial oxygen consumption (r = 0.749; p < 0. 001), and coronary blood flow (r = 0.645; p = 0.003), but inversely with coronary sinus oxygen content (r = -0.633; p = 0.004), which was significantly decreased in IDCM patients (IDCM 4.68 (1.05) v controls 6.70 (1.06) vol%; p = 0.003). CONCLUSIONS: The coronary circulation in patients with IDCM is exposed to an increased endothelin load. ET-1 concentrations correlate with functional deterioration. A decrease of the coronary sinus content of oxygen suggests a mismatch between coronary blood flow and metabolic demand. Thus, ET-1 might be a marker of a disequilibrium between myocardial oxygen demand and coronary blood flow in IDCM.

Aorta↗