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Biomedical subjects

L Tellmann

Publications and source records attributed to L Tellmann.

18 recordsLinked to original sources
PubMed2002

Conscious and subconscious sensorimotor synchronization--prefrontal cortex and the influence of awareness.

One of the most compelling challenges for modern neuroscience is the influence of awareness on behavior. We studied prefrontal correlates of conscious and subconscious motor adjustments to changing auditory rhythms using regional cerebral blood flow measurements. At a subconscious level, movement adjustments were performed employing bilateral ventral mediofrontal cortex. Awareness of change without explicit knowledge of the nature of change led to additional ventral prefrontal and premotor but not dorsolateral prefrontal activations. Only fully conscious motor adaptations to a changing rhythmic pattern showed prominent involvement of anterior cingulate and dorsolateral prefrontal cortex. These results demonstrate that while ventral prefrontal areas may be engaged in motor adaptations performed subconsciously, only fully conscious motor control which includes motor planning will involve dorsolateral prefrontal cortex.

Acoustic Stimulation↗
PubMed2002

Brain systems engaged in encoding and retrieval of word-pair associates independent of their imagery content or presentation modalities.

In this study, we aimed to characterize commonalities and differences of activation patterns during verbal episodic memory processes across different presentation modalities (visual or auditory) and different imagery content (low or high) of the presented verbal memory items. Twelve right-handed normal male volunteers took part in the study. Each subject underwent six O-15-butanol positron emission tomography scans. In six of the subjects the verbal material was presented visually, and in six subjects auditorily. The subjects had to encode and retrieve two sets of 12 word-pair associates of high (set 1) or low (set 2) imagery content (not semantically related). The presentation of nonsense words served as reference condition. Images were analyzed with statistical parametric mapping. Conjunction analysis was used to identify commonalities, and cognitive subtraction analysis was used to identify differences. The use of conjunction analyses enabled us to identify commonly activated regions involved in episodic encoding and retrieval of verbal material irrespective of the presentation modality or the imagery content. Our results add further evidence to recent findings that bilateral prefrontal activations are important for episodic retrieval and thus the role of the left prefrontal cortex has been underestimated during episodic retrieval. Furthermore, our results support the idea of functionally segregated areas in the prefrontal cortex. Finally, our results provide strong evidence that mesial parietal cortex (precuneus) involvement is not restricted to processes involving imagery.

Adult↗
PubMed2001

The motion aftereffect: more than area V5/MT? Evidence from 15O-butanol PET studies.

The motion aftereffect is a perceptual phenomenon which has been extensively investigated both psychologically and physiologically. Neuroimaging techniques have recently demonstrated that area V5/MT is activated during the perception of this illusion. The aim of this study was to test the hypothesis if a more broadly distributed network of brain regions subserves the motion aftereffect. To identify the neuronal structures involved in the perception of the motion aftereffect, regional cerebral blood flow (rCBF) measurements with positron emission tomography were performed in six normal volunteers. Data were analysed using SPM96. The motion-sensitive visual areas including area V5/MT were activated in both hemispheres. Additionally, the lateral parietal cortex bilaterally, the right dorsolateral prefrontal cortex, the anterior cingulate cortex and the left cerebellum showed significant increases in rCBF values during the experience of the waterfall illusion. In a further reference condition with identical attentional demand but no perception of a motion aftereffect elevated rCBF were found in these regions as well. In conclusion, our findings support the notion that the perceptual illusion of motion arises exclusively in the motion-sensitive visual area V5/MT. In addition, a more widespread network of brain regions including the prefrontal and parietal cortex is activated during the waterfall illusion which represents a non-motion aftereffect-specific subset of brain areas but is involved in more basic attentional processing and cognition.

Adult↗
PubMed2001

Neural correlates of religious experience.

The commonsense view of religious experience is that it is a preconceptual, immediate affective event. Work in philosophy and psychology, however, suggest that religious experience is an attributional cognitive phenomenon. Here the neural correlates of a religious experience are investigated using functional neuroimaging. During religious recitation, self-identified religious subjects activated a frontal-parietal circuit, composed of the dorsolateral prefrontal, dorsomedial frontal and medial parietal cortex. Prior studies indicate that these areas play a profound role in sustaining reflexive evaluation of thought. Thus, religious experience may be a cognitive process which, nonetheless, feels immediate.

Adult↗
PubMed2001

Interdependence of regional and global cerebral blood flow during visual stimulation: an O-15-butanol positron emission tomography study.

The authors investigated the influence of variations in global cerebral blood flow (gCBF) on regional flow changes during visual stimulation. Global flow was varied using different end-expiratory CO2 values (PETCO2) between 20 and 70 mm Hg. Visual stimulation was performed with a red LED-array flashing at 8 Hz. Blood flow was measured with 0-15-butanol, continuous arterial blood sampling, and positron emission tomography (PET). Global flow changes surpassed the published values of O-15-H2O studies, better fitting the results of the inert gas technique (gCBF at 20, 40, and 70 mm Hg PETCO2 +/- SD was 31 +/- 4, 48 +/- 13, and 160 +/- 50 mL 100 g(-1) min(-1), respectively). The relation between PETCO2 and CBF in the current study was best described by an exponential rather than a linear function. At low PETCO2, the activation-induced flow changes are moderately damped, whereas at high PETCO2, they are nearly lost (deltaCBF (+/-SD): 52% +/- 25%, 68% +/- 22%, 16% +/- 25% at PETCO2 = 20, 40, 70 mm Hg, respectively).

Adult↗
PubMed2000

Modulation of the neuronal circuitry subserving working memory in healthy human subjects by repetitive transcranial magnetic stimulation.

We studied the effect of repetitive transcranial magnetic stimulation (rTMS) on changes in regional cerebral blood flow (rCBF) as revealed by positron emission tomography (PET) while subjects performed a 2-back verbal working memory (WM) task. rTMS to the right or left dorsolateral prefrontal cortex (DLPFC), but not to the midline frontal cortex, significantly worsened performance in the WM task while inducing significant reductions in rCBF at the stimulation site and in distant brain regions. These results for the first time demonstrate the ability of rTMS to produce temporary functional lesions in elements of a neuronal network thus changing its distributed activations and resulting in behavioral consequences.

Adult↗
PubMed2000

Neural consequences of acting in near versus far space: a physiological basis for clinical dissociations.

We used PET to determine which brain regions are implicated when normal volunteers bisect horizontal lines and point to dots in near (peripersonal) or far (extrapersonal) space. Studies of line bisection in patients with right hemisphere lesions have shown that bisection performance can be severely impaired in either near or far space while remaining within normal limits in the other spatial domain. Likewise, clinical dissociations between pointing to objects in near and far space have been reported. The normal functional anatomy of these dissociations has not been demonstrated convincingly. Regional cerebral blood flow measurements using PET were carried out in 12 healthy right-handed male volunteers who bisected lines or pointed to dots in near or far space, using a laser pen. Subjects performing either task in near space showed neural activity in the left dorsal occipital cortex, left intraparietal cortex, left ventral premotor cortex and left thalamus. In far space, subjects performing either task showed activation of the ventral occipital cortex bilaterally and the right medial temporal cortex. These data provide physiological support for the clinically observed dissociations demonstrating that attending to and acting in near space differentially employs dorsal visuomotor processing areas, whereas attending to and acting in far space differentially draws on ventral visuoperceptual processing areas, even when the motor components of the tasks are identical when performed in the two spaces.

Adult↗
PubMed1999

Functional anatomy of intrinsic alertness: evidence for a fronto-parietal-thalamic-brainstem network in the right hemisphere.

Alertness, the most basic intensity aspect of attention, probably is a prerequisite for the more complex and capacity demanding domains of attention selectivity. Behaviorally, intrinsic alertness represents the internal (cognitive) control of wakefulness and arousal; typical tasks to assess optimal levels of intrinsic alertness are simple reaction time measurements without preceding warning stimuli. Up until now only parts of the cerebral network subserving alertness have been revealed in animal, lesion, and functional imaging studies. Here, in a 15O-butanol PET activation study in 15 right-handed young healthy male volunteers for this basic attention function we found an extended right hemisphere network including frontal (anterior cingulate-dorsolateral cortical)-inferior parietal-thalamic (pulvinar and possibly the reticular nucleus) and brainstem (ponto-mesencephalic tegmentum, possibly involving the locus coeruleus) structures, when subjects waited for and rapidly responded to a centrally presented white dot by pressing a response key with the right-hand thumb.

Adult↗
PubMed1999

Episodic retrieval activates the precuneus irrespective of the imagery content of word pair associates. A PET study.

The aim of this study was to evaluate further the role of the precuneus in episodic memory retrieval. The specific hypothesis addressed was that the precuneus is involved in episodic memory retrieval irrespective of the imagery content. Two groups of six right-handed normal male volunteers took part in the study. Each subject underwent six [15O]butanol-PET scans. In each of the six trials, the memory task began with the injection of a bolus of 1500 MBq of [15O]butanol. For Group 1, 12 word pair associates were presented visually, for Group 2 auditorily. The subjects of each group had to learn and retrieve two sets of 12 word pairs each. One set consisted of highly imaginable words and another one of abstract words. Words of both sets were not related semantically, representing 'hard' associations. The presentations of nonsense words served as reference conditions. We demonstrate that the precuneus shows consistent activation during episodic memory retrieval. Precuneus activation occurred in visual and auditory presentation modalities and for both highly imaginable and abstract words. The present study therefore provides further evidence that the precuneus has a specific function in episodic memory retrieval as a multimodal association area.

Acoustic Stimulation↗
PubMed1998

Role of the premotor cortex in recovery from middle cerebral artery infarction.

OBJECTIVE: To study the mechanisms underlying recovery from middle cerebral artery infarction in 7 patients with an average age of 53 years who showed marked recovery of hand function after acute severe hemiparesis caused by their first-ever stroke. INTERVENTIONS: Assessment of motor functions, transcranial magnetic stimulation, somatosensory evoked potentials, magnetic resonance imaging, and positron emission tomographic measurements of regional cerebral blood flow during finger movement activity. RESULTS: The infarctions involved the cerebral convexity along the central sulcus from the Sylvian fissure up to the hand area but spared the caudate nucleus, thalamus, middle and posterior portions of the internal capsule, and the dorsal part of the precentral gyrus in each patient. After recovery (and increase in motor function score of 57%, P<.001), the motor evoked potentials in the hand and leg muscles contralateral to the infarctions were normal, whereas the somatosensory evoked potentials from the contralateral median nerve were reduced. During fractionated finger movements of the recovered hand, regional cerebral blood flow increases occurred bilaterally in the dorsolateral and medial premotor areas but not in the sensorimotor cortex of either hemisphere. CONCLUSIONS: Motor recovery after cortical infarction in the middle cerebral artery territory appears to rely on activation of premotor cortical areas of both cerebral hemispheres. Thereby, short-term output from motor cortex is likely to be initiated.

Adult↗
PubMed1998

Encoding and retrieval in declarative learning: a positron emission tomography study.

We present neuroanatomical correlates of encoding and retrieval in an episodic memory task using visually presented highly imaginable word-pair associates. A total of 13 right-handed normal male volunteers took part in the study. Each subject underwent six (15)O-butanol PET scans. On each of the six trials the memory task began 30 s before the injection of a bolus of (15)O-butanol. The subjects had to learn and retrieve 12 word pairs (highly imaginable words, not semantically related, hard associations). The presentation of nonsense words served as a reference condition. Recall accuracy after 2-4 presentations was 66.1%+/-21.1 correct during the PET measurement so that scanning during the retrieval of word pair associates was appropriate to capture the brain activity associated with retrieval. The results obtained support the hypothesis of the presence of an asymmetric network consisting of distributed brain structures subserving associative memory. We show left dorsolateral prefrontal activation during the encoding of visually presented word pair associates, whereas retrieval led to bilateral frontal activation. Furthermore, the importance of the precuneus in the retrieval of highly imaginable word-pair associates using visual imagery as a mnemonic strategy is demonstrated.

Adult↗
PubMed1998

[O-15-butanol Pet activation study on the cerebral representation of declarative memory].

AIM: In this study, neuroanatomical correlates of encoding and retrieval in paired associate learning were evaluated with positron emission tomography using auditorily presented highly imaginable words. METHODS: Six right-handed normal male volunteers took part in the study. Each subject underwent six O-15-butanol PET scans. On each of the six trials the memory task began with the injection of a bolus of O-15-butanol. The subjects had to learn and retrieve twelve word pairs (highly imaginable words, not semantically related). The presentation of nonsense words served as reference condition. RESULTS: Recall accuracy after 2-4 presentations was high during the PET measurement. In both encoding and retrieval we found anterior cingulate activation. We show bilateral dorsolateral prefrontal activation during the encoding of auditorily presented word pair associates, whereas retrieval led to left frontal activation. Furthermore, we demonstrate the importance of the precuneus in the retrieval of highly imaginable word-pair associates. CONCLUSION: Our results support the hypothesis of the presence of distributed widespread brain structures subserving episodic declarative memory.

Adult↗
PubMed1997

Representations of graphomotor trajectories in the human parietal cortex: evidence for controlled processing and automatic performance.

The aim of this study was to identify the cerebral areas activated during kinematic processing of movement trajectories. We measured regional cerebral blood flow (rCBF) during learning, performance and imagery of right-hand writing in eight right-handed volunteers. Compared with viewing the writing space, increases in rCBF were observed in the left motor, premotor and frontomesial cortex, and in the right anterior cerebellum in all movement conditions, and the increases were related to mean tangential writing velocity. No rCBF increases occurred in these areas during imagery. Early learning of new ideomotor trajectories and deliberately exact writing of letters both induced rCBF increases in the cortex lining the right intraparietal sulcus. In contrast, during fast writing of overlearned trajectories and in the later phase of learning new ideograms the rCBF increased bilaterally in the posterior parietal cortex. Imagery of ideograms that had not been practised previously activated the anterior and posterior parietal areas simultaneously. Our results provide evidence suggesting that the kinematic representations of graphomotor trajectories are multiply represented in the human parietal cortex. It is concluded that different parietal subsystems may subserve attentive sensory movement control and whole-field visuospatial processing during automatic performance.

Adult↗
PubMed1996

Quantitation of regional cerebral blood flow with 15O-butanol and positron emission tomography in humans.

We describe the implementation and validation of a combined dynamic-autoradiographic approach for measuring the regional cerebral blood flow (rCBF) with 15O-butanol. From arterial blood data sampled at a rate of 1 s and list mode data of the cerebral radioactivity accumulated over 100 s, the time shift between blood and tissue curves, the dispersion constant DC, the partition coefficient p, and the CBF were estimated by least squares fitting. Using the fit results, a pixel-by-pixel parametrization of rCBF was computed for a single 40-s (autoradiographic) 15O-butanol uptake image. The mean global CBF found in 27 healthy subjects was 49 +/- 8 ml 100 g-1 min-1. Gray and white matter rCBF were 83 +/- 20 and 16 +/- 3 ml 100 g-1 min-1, respectively, with a corresponding partition coefficient p of 0.77 +/- 0.18 and 0.77 +/- 0.29 ml/g in both compartments. The quantitative images resulted in a significantly higher gray matter rCBF than the autoradiographic images.

Adult↗
PubMed1995

Large-scale plasticity of the human motor cortex.

The adult primate brain is capable of modifying rapidly the size of cortical receptive fields or motor output modules in response to altered synaptic input. We used positron emission tomography (PET) to map the regional cerebral blood flow changes related to voluntary finger movements in patients with tumours occupying the hand area of motor cortex. All patients showed activations solely outside the tumour. Compared with the unaffected side, the activations were shifted by 9-43 mm either along the mediolateral body representation of motor cortex or into premotor or parietal somatosensory cortex. These results provide evidence that slowly developing lesions can induce large-scale reorganization that is not confined to changes within the somatotopic body representation in motor cortex.

Adult↗
PubMed1994

Successive roles of the cerebellum and premotor cortices in trajectorial learning.

The structures of the human brain engaged during learning of unilateral trajectorial hand movements were mapped by measurements of regional cerebral blood flow. Trajectorial movement velocity accelerated moderately after short-term training p < 0.025 and increased further after long-term training p < 0.01. During the early phase of learning there was a significant activation p < 0.001 of the ipsilateral dentate nucleus. By contrast, after overlearning the premotor cortical areas in both cerebral hemispheres were maximally activated p < 0.001, while the dentate nucleus was no longer activated. It is suggested that learning of new movement trajectories involves the cerebellum, while overlearned trajectorial movements engage the premotor cortex.

Cerebellum↗
PubMed1994

Pharmacokinetics and radiation dose of oxygen-15 labelled butanol in rCBF studies in humans.

In this positron emission tomography (PET) study in humans we determined the pharmacokinetics and radiation dose of oxygen-15 labelled butanol, a recently introduced tracer for regional cerebral blood flow (rCBF). This report includes a description of the automated preparation of 15O-butanol which allows repetitive activation studies, each 15 min apart. Dynamic rCBF studies were extended by prolonged measurements up to 15 min after injection over different organs such as brain, liver, kidneys and bladder. All measurements were done with a whole-body PET camera PC4096-15WB. Based on the pharmacokinetic data in 13 subjects the radiation doses to single organs were calculated according to MIRD pamphlet No. 11 and the effective dose defined by ICRP 60 as an indicator of radiation dose to the total body. The liver received the highest radiation dose of about 2.2 mGy per 1500 MBq of injected 15O-butanol, which is the typical amount of administered tracer in one rCBF measurement. The dose to the kidneys was 1.6 mGy, to the stomach 0.8 mGy, and to the brain 0.16 mGy. The effective dose was 0.54 mGy, which was similar to that of H2(15)O, but lower than the effective dose from C15O2 in amounts typically applied in human rCBF studies.

Adult↗