Biomedical subjects

Jaana Hiltunen

Publications and source records attributed to Jaana Hiltunen.

9 recordsLinked to original sources

PubMed2007

Brain function during multi-trial learning in mild cognitive impairment: a PET activation study.

We explored functional brain changes with positron emission tomography (PET) in mild cognitive impairment (MCI) patients and elderly normal controls by employing an episodic memory task that included two successive encoding trials of semantically related word-pairs and final retrieval. Both groups demonstrated significant learning across the two trials. The control group showed predominantly left frontal activity during encoding, and right frontal plus left temporal activity during retrieval. However, the MCI patients recruited partly different brain regions. They failed to activate right frontal and left temporal areas during retrieval, and failed to show any different activation for encoding on the first and second trials, whereas the controls activated a region of posterior cingulate. There was indication of compensatory increases in rCBF of the occipital cortex during incremental learning and the left frontal lobe during retrieval in the patients. These results suggest different episodic memory processing in the MCI group, and a possible over-reliance on semantic processing. Subtle functional changes occur in the pre-Alzheimer brain before there are marked structural or behavioural abnormalities.

Aged↗

PubMed2006

Quantification of mechanical vibration during diffusion tensor imaging at 3 T.

Subjects sense clear mechanical vibrations during diffusion tensor imaging (DTI). These vibrations, likely resulting from diffusion-sensitizing gradients, have been assumed to be of the same strength and phase in all parts of the magnetic resonance imaging (MRI) scanner so that they could be ignored. However, our measurements, carried out from several parts of the MRI scanner and its surroundings using an optical laser-based interferometer, demonstrate an uneven distribution of mechanical vibrations within the scanner. The measurements were performed during DT scanning at 3 T, with various diffusion-weighting parameters, by positioning a phantom in the head coil and/or a human subject on the patient bed. The vibration-related movement was caused by the diffusion-sensitizing gradients and was maximally 0.5 mm with typical settings used in brain imaging. The compensation for eddy currents, done with gradients in our DTI sequence, increased the vibration level by a factor of 1.5 or more with diffusion-weighting parameter b = 1000 s/mm(2) and by a factor of 3 or more with b = 3000 s/mm(2). Mechanical vibrations stayed at an acceptable level with b < or = 1000 s/mm(2), resulting in additional signal losses of 5-17%. Vibration levels might be reduced by adjusting imaging parameters, by modifying the gradient waveforms in the DTI sequence, and by redesigning the mechanics of patient bed to effectively dampen the movements.

Animals↗

PubMed2006

Functional brain imaging, clinical and neurophysiological outcome of visual rehabilitation in a chronic stroke patient.

PURPOSE: To study rehabilitation outcome in a chronic visual field defect patient using positron emission tomography (PET) imaging, clinical, and neurophysiological measures. METHODS: A patient with chronic visual field defect was rehabilitated using a computer program over a three-month period. Evaluations of rehabilitation effects were done before and after training, and after a three-month follow-up with perimetry, visual evoked potentials (VEP), subjective questionnaire, and PET activation studies of regional cerebral blood flow (rCBF). RESULTS: In perimetry, the visual field increased during the training, and the patient also experienced subjective improvement. In VEP, a previously absent P100 component was identified after the training. In PET, increases in rCBF were diffuse immediately after the training, and more occipital after the late follow-up. A significant positive correlation between the increase in rCBF and improvement in clinical measures was found in the lingual gyrus in the contralesional hemisphere. CONCLUSIONS: All clinical measures showed improvement after rehabilitation, and this was maintained during the follow-up. In PET, a more generalized effect, found at the beginning, later concentrated in the occipital cortex. The results suggest that visual training may cause plastic changes in the brain, and that these changes can be detected both with clinical measures and with functional imaging.

Brain↗

PubMed2005

Brain correlates of subjective reality of physically and psychologically induced pain.

Meaningful behavior requires successful differentiation of events surfacing from one's mind from those arising from the external world. Such judgements may be especially demanding during pain because of the strong contribution from psychological factors to this experience. It is unknown how the subjective reality of pain (SRP) is constructed in the human brain, and neuronal mechanisms of the subjective reality are poorly understood in general. To address these questions, 14 suggestion-prone healthy subjects rated reality of pain that was induced either by laser pulses to the skin or by hypnotic suggestion during functional MRI. Both pain states were associated with activation of the brain's pain circuitry. During laser stimulation, the sensory parts of this circuitry were activated more strongly, and their activation strengths correlated positively with the SRP. During suggestion-induced pain, the reality estimates were lower and correlated positively with activation strengths in the rostral and perigenual anterior cingulate cortex and in the pericingulate regions of the medial prefrontal cortex; a similar trend was evident during laser-induced pain. These findings support the view that information about sensory-discriminative characteristics of pain contributes to the SRP. Differences in such information between physically and psychologically induced pain, however, could be quantitative rather than qualitative and therefore insufficient for judging the reality of pain without knowledge about the source of this information. The medial prefrontal cortex is a likely area to contribute to such source monitoring.

Adult↗

PubMed2005

Regression analysis utilizing subjective evaluation of emotional experience in PET studies on emotions.

A methodological study on subject-specific regression analysis (SSRA) exploring the correlation between the neural response and the subjective evaluation of emotional experience in eleven healthy females is presented. The target emotions, i.e., amusement and sadness, were induced using validated film clips, regional cerebral blood flow (rCBF) was measured using positron emission tomography (PET), and the subjective intensity of the emotional experience during the PET scanning was measured using a category ratio (CR-10) scale. Reliability analysis of the rating data indicated that the subjects rated the intensity of their emotional experience fairly consistently on the CR-10 scale (Cronbach alphas 0.70-0.97). A two-phase random-effects analysis was performed to ensure the generalizability and inter-study comparability of the SSRA results. Random-effects SSRAs using Statistical non-Parametric Mapping 99 (SnPM99) showed that rCBF correlated with the self-rated intensity of the emotional experience mainly in the brain regions that were identified in the random-effects subtraction analyses using the same imaging data. Our results give preliminary evidence of a linear association between the neural responses related to amusement and sadness and the self-evaluated intensity of the emotional experience in several regions involved in the emotional response. SSRA utilizing subjective evaluation of emotional experience turned out a feasible and promising method of analysis. It allows versatile exploration of the neurobiology of emotions and the neural correlates of actual and individual emotional experience. Thus, SSRA might be able to catch the idiosyncratic aspects of the emotional response better than traditional subtraction analysis.

Adolescent↗

PubMed2005

Diffusion tensor imaging and tractography of distal peripheral nerves at 3 T.

OBJECTIVE: We studied whether distal peripheral nerves could be imaged using quantitative diffusion tensor imaging (DTI) with a 3-T MRI scanner, and visualized using tractography. METHODS: Altogether 6 healthy subjects were studied. The diffusion was quantified with apparent diffusion coefficient (ADC) and fractional anisotropy (FA) maps, and the direction of main diffusivity was visualized with color-coded orientation maps and tractography. RESULTS: We present the first DTI and tractography results of human distal peripheral nerves. The courses of median, ulnar, and radial nerves in the upper limb and of tibial and peroneal nerves in the lower limb were first analyzed quantifying ADC and FA, and then visualized in 3D with tractography. Tractography illustrated nicely the 3D courses of both upper and lower limb nerves which were reliably distinguished from the surrounding muscle tissue and ligaments. CONCLUSIONS: Quantitative DTI and tractography can be used to image and visualize distal peripheral nerves. SIGNIFICANCE: DTI is a quantitative method that could provide useful information for the diagnosis and follow-up of nerve lesions, entrapments, and regeneration. Peripheral nerves as well-delineated structures also containing abundant branching into bundles of different diameters, could be used as 'living phantoms' for testing and validating different tractography methods.

Adult↗

PubMed2004

Cortical activation during a spatiotemporal tactile comparison task.

Tactile sensory memory is needed to infer shape or motion from the spatiotemporal pattern of sensory input during manual exploration. Here we applied triplets of pressure pulses to the fingertips of subjects who were asked to respond when successive triplets were the same (COMPARE task) or when a particular stimulus was included in a triplet (CONTROL task). Stimulus sequences (30 s) alternated with rest blocks (30 s) and functional magnetic resonance images (fMRIs) were acquired in a 1.5-T scanner. During the COMPARE task, we found enhanced activation in inferior parietal cortex, supplementary motor area (SMA), and right dorsolateral prefrontal cortex (DLPFC). Activation of DLPFC is likely to be related to the attempt to memorize the stimulus sequences and activations of SMA and inferior parietal cortex to the analysis of temporospatial tactile patterns and, more generally, to guidance of haptic exploration. In addition, task-specific activation was seen in anterior cingulate gyrus, possibly related to the high mental effort required by the comparison task. Our rhythmic tactile stimulus as such, without any task-specific enhancement, activated also left cerebellum and (mainly left) putamen, supporting the idea that these structures are related to perception of temporal order of tactile stimuli.

Adult↗

PubMed2003

Naming multiple objects: neural correlates as measured by positron emission tomography.

The aim of this study was to examine the neural substrates of multi-object naming by positron emission tomography in normals. Multi-object naming is used in a technique called contextual priming (CP) to elicit contextual effects on picture naming through systematic manipulation of the relatedness of to-be-named pictures in an array. Inhibitory and facilitatory effects of CP on naming have been used both to highlight the inner dynamics of the normal word retrieval system and to treat naming difficulties caused by acquired anomia. Because of the complexity of the CP technique, it is unclear whether it merely reflects lexical retrieval or whether it also recruits general cognitive resources such as attentional control and response selection to a significant degree. When compared with a baseline situation in which colored circles were named, multi-object naming elicited increased blood flow in the occipital lobe and in the left inferior temporal and fusiform gyri. These areas have been related to visual pattern recognition and semantic access, and the pattern of activation is in line with previous functional imaging studies on single picture naming. In conclusion, multi-object naming does not appear to activate brain regions beyond those needed for single object naming. These findings thus provide independent evidence for the claim that CP is a valid paradigm for the study of word production proper.

Adult↗

PubMed2002

Different brain activation patterns during production of animals versus artefacts: a PET activation study on category-specific processing.

To study neural correlates of category-specific processing, we measured relative cerebral blood flow changes by PET (oxygen-15) in young healthy subjects while they produced exemplars of animals or artefacts to written subcategory prompts. In comparison to a baseline (word reading), production of animal names elicited increased rCBF in the right inferior temporal region. This fits to recent lesion data on semantic impairment with animals, as well as imaging data on object recognition and semantic retrieval. In our study, it may represent an involvement of visual imagery in generation of animal names. In contrast, production of artefact names elicited increased rCBF in frontoparietal regions previously related to attention and mental effort.

Adult↗