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T Paus

Publications and source records attributed to T Paus.

47 records · Page 3Linked to original sources
PubMed1995

Extraretinal modulation of cerebral blood flow in the human visual cortex: implications for saccadic suppression.

1. Extraretinal modulation of neuronal activity in the human brain was assessed indirectly by measuring changes in regional cerebral blood flow (rCBF) during the execution of large horizontal saccades in complete darkness. With the use of positron emission tomography, rCBF was measured in 9 volunteers as they made 40, 60, 80, 100, 110, 120, or 140 saccades during 60-s scans. 2. With increasing numbers of saccades, rCBF increased in the following oculomotor structures: the frontal eye field, the superior colliculus, and the cerebellar vermis. In parallel to these rCBF increases, rCBF decreased in the striate cortex, adjacent extrastriate cortex, and the parietal cortex. 3. The observed rCBF decreases most likely indicate a decline in the net amount of excitatory neurotransmission in the visual cortex and, as such, may represent a neural substrate of saccadic suppression.

Analysis of Variance↗
PubMed1993

Role of the human anterior cingulate cortex in the control of oculomotor, manual, and speech responses: a positron emission tomography study.

1. Two experiments were aimed at investigating the functional organization of the human anterior cingulate cortex (ACC) in relation to higher-order motor control. 2. The 15O-labeled H2O bolus method was used to measure relative changes of regional cerebral blood flow (rCBF) in 18 healthy human subjects as they performed oculomotor, manual, or speech tasks. 3. Task-specific rCBF changes were obtained in distinct subregions of the ACC, depending on the output system employed. The oculomotor and the manual task-related foci were found in the rostral and caudal regions of the ACC, respectively, whereas the speech foci were localized within two cingulate subregions, the intermediate dorsal and the rostral ACC. 4. In the manual tasks, two groups of activation foci could be distinguished, one just behind and the other just in front of the vertical plane traversing the anterior commissure. 5. The above pattern of rCBF changes was observed only if there was concomitant activation within the lateral prefrontal cortex (except for the posterior group of foci obtained in the manual tasks). 6. The localization of output-specific rCBF changes within the human ACC is consistent with the known somatotopic organization of the cingulate cortex in the monkey. 7. It is tentatively proposed that the ACC participates in motor control by facilitating the execution of the appropriate responses and/or suppressing the execution of the inappropriate ones. Such a modulatory effect would be of particular importance when behavior has to be modified in new and challenging situations.

Adult↗
PubMed1991

Two modes of central gaze fixation maintenance and oculomotor distractibility in schizophrenics.

Distractibility defined operationally as a lack of stability in central-gaze fixation has been studied using two different oculomotor tasks that require the suppression of reflexive saccades triggered by the sudden appearance of novel, peripheral visual stimuli. In the first task ('Instructed'), maintenance of central gaze fixation was based on verbal instruction, whereas, in the second task ('Non-Instructed'), it was based upon a foveating mechanism maintained by sensory stimulation during the performance of a categorization task. 15 schizophrenics and 20 healthy control subjects were tested in the two tasks. Schizophrenics made more saccades than control subjects in the Instructed task only. The Instructed task saccade rate correlated significantly with scores on neuropsychological tests sensitive to frontal lobe dysfunction. Because the type of deficit observed in schizophrenics resembled that previously seen in patients with unilateral lesions of the ventrolateral convexity of frontal lobe, frontal lobe dysfunction was proposed as underlying the high task-specific distractibility of schizophrenics.

Adult↗
PubMed1991

Medial vs lateral frontal lobe lesions and differential impairment of central-gaze fixation maintenance in man.

The ability to maintain central-gaze fixation was studied in 35 patients with unilateral frontal lobe lesions. The stability of central-gaze fixation was tested in 2 oculomotor tasks requiring the suppression of reflexive saccades triggered by the sudden appearance of novel, peripheral visual stimuli. In the first task ('Instructed'), maintenance of gaze fixation was based on verbal instruction, whereas, in the second task ('Non-instructed'), it was based upon a foveating mechanism maintained by sensory stimulation during the performance of a categorization task. Patients with frontal lobe lesions were classified into 3 groups: a ventrolateral (n = 18), a dorsolateral (n = 10) and a medial (n = 7) group. The control group consisted of 20 healthy subjects. In the Non-instructed task, no group differences were found in the rate of reflexive saccades. Thus, lesions of the frontal lobe did not affect reactivity to extraneous stimuli per se. The only exception to this rule was the group of patients with ventrolateral lesions in the left frontal lobe, in which a higher number of reflexive saccades directed to the contralateral hemifield was observed. In the Instructed task, 2 different patterns of deficit in suppression of reflexive saccades were found. First, a bidirectional deficit was noted in the ventrolateral group, which might be attributed to an impairment in either maintaining a selected program of behaviour 'on-line' or suppressing inappropriate alternatives interfering with that program. Second, a unidirectional deficit in voluntary suppression of reflexive saccades triggered from within the contralateral hemifield was observed in the medial group. It is suggested that this type of deficit may reflect malfunctioning of the supplementary motor area--anterior cingulate system involved in the suppression of externally triggered interfering programs. Finally, no significant impairment was found in the dorsolateral group.

Adult↗
PubMed1990

Development of an ability to maintain verbally instructed central gaze fixation studied in 8- to 10-year-old children.

Development of an ability to maintain verbally instructed central gaze fixation was studied in 8-, 9- and 10-year-old boys. The stability of central gaze fixation was tested by the sudden appearance of a novel, peripheral stimulus triggering reflexive saccade. In Experiment I, the ability to maintain verbally instructed central gaze fixation upon nonsense geometrical pattern was found to be equal in 8 and 9 years of life. This ability increased markedly between 9 and 10 years of age. Gaze fixation upon gradually appearing shapes during a TV-like game reducing volitional effort of subject was, however, equal in all age groups. Concentration of attention upon central stimulus as reflected by saccade latency (Experiment I) and P3-N3 amplitude of evoked potentials to peripheral flashes (Experiment II) was equal in both tasks in 8-year-olds. In contrast, higher concentration of attention upon meaningful central stimulus presented during the TV-like game was found in 9- as well as in 10-year-old boys. Developmental changes of the ability to maintain verbally instructed central gaze fixation might be related to the late structural maturation of frontal cortex.

Attention↗
PubMed1989

The development of sustained attention in children might be related to the maturation of frontal cortical functions.

The relationship between the development of sustained attention and the ability to inhibit responding to external stimuli was investigated in seventy five children, 8, 10 and 12 years old. An important period in the development of both functions is between 8 and 10 years of age. A positive correlation was found between the number of signals detected (sustained attention) and the number of successfully suppressed reflexive saccades to the peripherally located target (the ability to inhibit responding to external stimuli).

Attention↗
PubMedDate not supplied

Human cingulate and paracingulate sulci: pattern, variability, asymmetry, and probabilistic map.

Recent advances in functional neuroimaging of the human cerebral cortex revived interest in the study of the cortical morphology at both macro- and microscopic levels. By means of high-resolution magnetic resonance imaging (MRI), in vivo images of the human brain can be acquired and used to aid localization of the functional maps. The goal of the present study was to determine variability in the occurrence and location of the cingulate sulcus (CS) and the paracingulate sulcus (PCS). Brain MRIs of 247 healthy young volunteers were obtained and transformed into a standardized stereotaxic space (Talairach and Tournoux, 1988). The CS and PCS were marked in 494 hemispheres using software capable of real-time movement through a 3-D volume. The markers were used to generate a probabilistic map of the CS and PCS. The individual MRI images were also evaluated for the presence and location of the following morphological features: the continuity of the CS, the presence of vertically oriented branches of the CS, the presence of the PCS, and the presence of the intralimbic sulcus. The results revealed considerable variability in the location of some of the above morphological features and a striking hemispheric asymmetry in the prominence of the PCS. The results of four previous blood-flow activation studies of speech control were used to illustrate the relevance of our morphological findings for functional neuroimaging of the human anterior cingulate cortex.

Adolescent↗
PubMedDate not supplied

A four-dimensional probabilistic atlas of the human brain.

The authors describe the development of a four-dimensional atlas and reference system that includes both macroscopic and microscopic information on structure and function of the human brain in persons between the ages of 18 and 90 years. Given the presumed large but previously unquantified degree of structural and functional variance among normal persons in the human population, the basis for this atlas and reference system is probabilistic. Through the efforts of the International Consortium for Brain Mapping (ICBM), 7,000 subjects will be included in the initial phase of database and atlas development. For each subject, detailed demographic, clinical, behavioral, and imaging information is being collected. In addition, 5,800 subjects will contribute DNA for the purpose of determining genotype- phenotype-behavioral correlations. The process of developing the strategies, algorithms, data collection methods, validation approaches, database structures, and distribution of results is described in this report. Examples of applications of the approach are described for the normal brain in both adults and children as well as in patients with schizophrenia. This project should provide new insights into the relationship between microscopic and macroscopic structure and function in the human brain and should have important implications in basic neuroscience, clinical diagnostics, and cerebral disorders.

Adolescent↗