3 results on '"Dietz, Martin J."'
Search Results
2. Activated N‐methyl‐D‐aspartate receptor ion channels detected in focal epilepsy with [18F]GE‐179 positron emission tomography.
- Author
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Vibholm, Ali K., Dietz, Martin J., Beniczky, Sándor, Christensen, Jakob, Højlund, Andreas, Jacobsen, Jan, Bender, Dirk, Møller, Arne, and Brooks, David J.
- Subjects
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POSITRON emission tomography , *PARTIAL epilepsy , *METHYL aspartate receptors , *MAGNETIC resonance imaging , *ION channels - Abstract
Summary: Objective: Imaging activated glutamate N‐methyl‐D‐aspartate receptor ion channels (NMDAR‐ICs) using positron emission tomography (PET) has proved challenging due to low brain uptake, poor affinity and selectivity, and high metabolism and dissociation rates of candidate radioligands. The radioligand [18F]GE‐179 is a known use‐dependent marker of NMDAR‐ICs. We studied whether interictal [18F]GE‐179 PET would detect foci of abnormal NMDAR‐IC activation in patients with refractory focal epilepsy. Methods: Ten patients with refractory focal epilepsy and 18 healthy controls had structural magnetic resonance imaging (MRI) followed by a 90‐min dynamic [18F]GE‐179 PET scan with simultaneous electroencephalography (EEG). PET and EEG findings were compared with MRI and previous EEGs. Standard uptake value (SUV) images of [18F]GE‐179 were generated and global gray matter uptake was measured for each individual. To localize focal increases in uptake of [18F]GE‐179, the individual SUV images were interrogated with statistical parametric mapping in comparison to a normal database. Additionally, individual healthy control SUV images were compared with the rest of the control database to determine their prevalence of increased focal [18F]GE‐179 uptake. Results: Interictal [18F]GE‐179 PET detected clusters of significantly increased binding in eight of 10 patients with focal epilepsy but none of the controls. The number of clusters of raised [18F]GE‐179 uptake in the patients with epilepsy exceeded the focal abnormalities revealed by the simultaneously recorded EEG. Patients with extensive clusters of raised [18F]GE‐179 uptake showed the most abnormal EEGs. Significance: Detection of multiple foci of abnormal NMDAR‐IC activation in 80% of our patients with refractory focal epilepsy using interictal [18F]GE‐179 PET could reflect enhanced neuronal excitability due to chronic seizure activity. This indicates that chronic epileptic activity is associated with abnormal NMDAR ion channel activation beyond the initial irritative zones. [18F]GE‐179 PET could be a candidate marker for identifying pathological brain areas in patients with treatment‐resistant focal epilepsy. [ABSTRACT FROM AUTHOR]
- Published
- 2021
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3. Anterior insula coordinates hierarchical processing of tactile mismatch responses
- Author
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Allen, Micah, Fardo, Francesca, Dietz, Martin J., Hillebrandt, Hauke, Friston, Karl J., Rees, Geraint, and Roepstorff, Andreas
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Adult ,Cerebral Cortex ,Male ,Predictive coding ,DCM ,Cognitive Neuroscience ,Models, Neurological ,fMRI ,Middle Aged ,Magnetic Resonance Imaging ,Article ,Young Adult ,Neurology ,Touch Perception ,Neural Pathways ,Image Processing, Computer-Assisted ,Humans ,Female - Abstract
The body underlies our sense of self, emotion, and agency. Signals arising from the skin convey warmth, social touch, and the physical characteristics of external stimuli. Surprising or unexpected tactile sensations can herald events of motivational salience, including imminent threats (e.g., an insect bite) and hedonic rewards (e.g., a caressing touch). Awareness of such events is thought to depend upon the hierarchical integration of body-related mismatch responses by the anterior insula. To investigate this possibility, we measured brain activity using functional magnetic resonance imaging, while healthy participants performed a roving tactile oddball task. Mass-univariate analysis demonstrated robust activations in limbic, somatosensory, and prefrontal cortical areas previously implicated in tactile deviancy, body awareness, and cognitive control. Dynamic Causal Modelling revealed that unexpected stimuli increased the strength of forward connections along a caudal to rostral hierarchy—projecting from thalamic and somatosensory regions towards insula, cingulate and prefrontal cortices. Within this ascending flow of sensory information, the AIC was the only region to show increased backwards connectivity to the somatosensory cortex, augmenting a reciprocal exchange of neuronal signals. Further, participants who rated stimulus changes as easier to detect showed stronger modulation of descending PFC to AIC connections by deviance. These results suggest that the AIC coordinates hierarchical processing of tactile prediction error. They are interpreted in support of an embodied predictive coding model where AIC mediated body awareness is involved in anchoring a global neuronal workspace., Highlights • A body-related network of thalamic, somatosensory, insular, cingulate, and prefrontal areas responded to tactile oddballs. • Dynamic Causal Modelling revealed oddball stimuli modulated an ascending rostral-to-caudal hierarchy between these areas. • Within this feed-forward flow, only anterior insula showed reciprocal increases in connectivity with somatosensory cortex. • Subjective deviance detection ratings predicted the strength of feedback from prefrontal cortex to anterior insula • These results provide preliminary evidence for the newly emerging theory of embodied predictive coding.
- Published
- 2015
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