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Christian Gaser

Publications and source records attributed to Christian Gaser.

14 recordsLinked to original sources
PubMed2026

Mapping Focal and Generalized Effects of Common Genetic Variants on Human Brain Structure.

Genome-wide association studies (GWAS) have advanced the quest to understand how specific genetic variants influence human brain structure and function. Recent work has identified hundreds of common variants associated with subcortical brain volumes, sparking interest in how these genetic markers overlap across brain networks. While this can be estimated by hierarchical clustering of the genetic correlation matrix to identify modular patterns of shared architecture, no brain-wide maps of these effects are available. To address this, we computed polygenic scores (PGS) from loci associated with ten brain volume regions of interest (ROIs): nine major subcortical structures and intracranial volume, with each locus weighted by its association with regional volume. In an independent sample from the discovery GWAS, we performed large-scale segmentation of 3D volumetric T1-weighted MRI scans using voxel-based morphometry (VBM) to map 3D profile of regions where gray matter volume (GMV) was associated with each PGS. We found statistically significant, localized effects for PGS defined for the amygdala, thalamus, and basal ganglia, but PGS for brainstem volume was associated with widespread differences throughout the brain. These brain-wide maps reveal patterns consistent with both localized and distributed genetic influences, offering a novel approach to interpret the genomic architecture of brain structure.

GWAS↗
PubMed2006

Increased local gyrification mapped in Williams syndrome.

Applying a recently developed method to analyze gyrification with excellent spatial resolution across thousands of points across the lateral and medial cortical surface, we mapped differences in cortical surface anatomy between subjects with Williams syndrome (WS; n=42) and an age-matched sample of healthy subjects (n=40). WS subjects showed increased gyrification bilaterally in occipital regions and over the cuneus. Differences were more pronounced in the left hemisphere than in the right, with additional regions of increased gyrification in WS in the left precuneus, posterior and anterior cingulate, paracentral and mesial frontal lobe. No cortical area was significantly more convoluted in healthy subjects relative to the WS subjects. On the lateral surfaces, the direction and pattern of gyrification asymmetries were similar in WS subjects and controls; posterior brain regions had greater gyrification in the left hemisphere, while anterior brain regions showed greater gyrification in the right hemisphere. On the medial surfaces, control subjects and WS individuals differed considerably with respect to the degree but also direction of gyrification asymmetry. Our findings confirm and extend previous studies measuring cortical complexity at the global whole-brain or hemispheric levels. The observed gyrification abnormalities in individuals with WS might be related to dysfunctions in neuronal circuits and consequently contribute to the distinct cognitive and behavioral profile accompanying the disorder.

Adolescent↗
PubMed2006

Temporal and spatial dynamics of brain structure changes during extensive learning.

The current view regarding human long-term memory as an active process of encoding and retrieval includes a highly specific learning-induced functional plasticity in a network of multiple memory systems. Voxel-based morphometry was used to detect possible structural brain changes associated with learning. Magnetic resonance images were obtained at three different time points while medical students learned for their medical examination. During the learning period, the gray matter increased significantly in the posterior and lateral parietal cortex bilaterally. These structural changes did not change significantly toward the third scan during the semester break 3 months after the exam. The posterior hippocampus showed a different pattern over time: the initial increase in gray matter during the learning period was even more pronounced toward the third time point. These results indicate that the acquisition of a great amount of highly abstract information may be related to a particular pattern of structural gray matter changes in particular brain areas.

Adult↗
PubMed2006

Improvement-related functional plasticity following pitch memory training.

Functional activation patterns of an auditory working memory task were examined prior to and after 5 days of training (1 h/day). A control group with no training was scanned twice at the same intervals to assess test-retest effects. Based on behavioral improvement scores, the training group (n = 14) was divided into "Strong-Learners (SL)" and "Weak-Learners (WL)". No significant functional or structural brain differences were seen between the SL and WL groups prior to training. Imaging contrasts comparing post- with pre-training sessions showed a significant signal increase in the left Heschl's gyrus (HG) as well as in the left posterior superior temporal and supramarginal gyrus for the SL group, while the WL group showed significant signal increases in the left HG and anterior insular cortex as well as in a lingual-orbitofrontal-parahippocampal network. The test-retest analysis in the control group revealed only minimal signal increases in a right dorsolateral prefrontal region. A random effects analysis comparing the SL group with the WL group using the post- and pre-training contrast images showed increased activation only in the left supramarginal gyrus but not in HG. The importance of HG in pitch discrimination has been established in previous studies. The pitch memory component differentiated our task from a straight pitch discrimination task. It is most likely that the activation of the SMG reflects its importance in the short-term storage of auditory material, and it was this activation that best differentiated between subjects' levels of performance.

Adult↗
PubMed2006

Magnetic resonance-based morphometry: a window into structural plasticity of the brain.

PURPOSE OF REVIEW: In contrast to traditional anatomical and pathological methods, magnetic resonance morphometry of the brain allows the in-vivo study of temporal changes in brain morphology and the correlation of brain morphology with brain function. Magnetic resonance morphometry has thereby recently emerged as one of the most promising fields in clinical neuroscience. This review covers the last 3 years, which have witnessed remarkable progress in this alluring new field. RECENT FINDINGS: Next to the detection of structural differences in grey and white matter in a number of brain diseases, a very important recent finding of magnetic resonance-based morphometry is the discovery of the brain's ability to alter its shape within weeks, reflecting structural adaptation to physical and mental activity. Consequently, magnetic resonance morphometry promises to be a powerful method to study disease states of the brain and to track the effects of novel therapies. SUMMARY: Despite these fascinating prospects, the results of morphometric studies are still dependent on the properties of the individual magnetic resonance scanner, which renders pooling of data almost impossible. It is also not known what the structural plasticity is based on at the histological or cellular level. Once these obstacles are overcome, magnetic resonance-based morphometry will become a powerful method for multicenter and therapeutic trials of several brain diseases.

Brain↗
PubMed2004

Neuroanatomy of "hearing voices": a frontotemporal brain structural abnormality associated with auditory hallucinations in schizophrenia.

Auditory hallucinations are a frequent symptom in schizophrenia. While functional imaging studies have suggested the association of certain patterns of brain activity with sub-syndromes or single symptoms (e.g. positive symptoms such as hallucinations), there has been only limited evidence from structural imaging or post-mortem studies. In this study, we investigated the relation of local brain structural deficits to severity of auditory hallucinations, particularly in perisylvian areas previously reported to be involved in auditory hallucinations. In order to overcome certain limitations of conventional volumetric methods, we used deformation-based morphometry (DBM), a novel automated whole-brain morphometric technique, to assess local gray and white matter deficits in structural magnetic resonance images of 85 schizophrenia patients. We found severity of auditory hallucinations to be significantly correlated (P < 0.001) with volume loss in the left transverse temporal gyrus of Heschl (primary auditory cortex) and left (inferior) supramarginal gyrus, as well as middle/inferior right prefrontal gyri. This demonstrates a pattern of distributed structural abnormalities specific for auditory hallucinations and suggests hallucination-specific alterations in areas of a frontotemporal network for processing auditory information and language.

Adult↗
PubMed2004

Ventricular enlargement in schizophrenia related to volume reduction of the thalamus, striatum, and superior temporal cortex.

OBJECTIVE: Enlargement of the lateral ventricles is among the most frequently reported macroscopic brain structural changes in schizophrenia, although variable in extent and localization. The authors investigated whether ventricular enlargement is related to regionally specific volume loss. METHOD: High-resolution magnetic resonance imaging scans from 39 patients with schizophrenia were analyzed with deformation-based morphometry, a voxel-wise whole brain morphometric technique. RESULTS: Significant negative correlations with the ventricle-brain ratio were found for voxels in the left and right thalamus and posterior putamen and in the left superior temporal gyrus and insula. CONCLUSIONS: Thalamic shrinkage, especially of medial nuclei and the adjacent striatum and insular cortex, appear to be important contributors to ventricular enlargement in schizophrenia.

Adolescent↗
PubMed2003

Brain structures differ between musicians and non-musicians.

From an early age, musicians learn complex motor and auditory skills (e.g., the translation of visually perceived musical symbols into motor commands with simultaneous auditory monitoring of output), which they practice extensively from childhood throughout their entire careers. Using a voxel-by-voxel morphometric technique, we found gray matter volume differences in motor, auditory, and visual-spatial brain regions when comparing professional musicians (keyboard players) with a matched group of amateur musicians and non-musicians. Although some of these multiregional differences could be attributable to innate predisposition, we believe they may represent structural adaptations in response to long-term skill acquisition and the repetitive rehearsal of those skills. This hypothesis is supported by the strong association we found between structural differences, musician status, and practice intensity, as well as the wealth of supporting animal data showing structural changes in response to long-term motor training. However, only future experiments can determine the relative contribution of predisposition and practice.

Adolescent↗
PubMed2003

Functional anatomy of pitch memory--an fMRI study with sparse temporal sampling.

Auditory functional magnetic resonance imaging tasks are challenging since the MR scanner noise can interfere with the auditory stimulation. To avoid this interference a sparse temporal sampling method with a long repetition time (TR = 17 s) was used to explore the functional anatomy of pitch memory. Eighteen right-handed subjects listened to a sequence of sine-wave tones (4.6 s total duration) and were asked to make a decision (depending on a visual prompt) whether the last or second to last tone was the same or different as the first tone. An alternating button press condition served as a control. Sets of 24 axial slices were acquired with a variable delay time (between 0 and 6 s) between the end of the auditory stimulation and the MR acquisition. Individual imaging time points were combined into three clusters (0-2, 3-4, and 5-6 s after the end of the auditory stimulation) for the analysis. The analysis showed a dynamic activation pattern over time which involved the superior temporal gyrus, supramarginal gyrus, posterior dorsolateral frontal regions, superior parietal regions, and dorsolateral cerebellar regions bilaterally as well as the left inferior frontal gyrus. By regressing the performance score in the pitch memory task with task-related MR signal changes, the supramarginal gyrus (left>right) and the dorsolateral cerebellum (lobules V and VI, left>right) were significantly correlated with good task performance. The SMG and the dorsolateral cerebellum may play a critical role in short-term storage of pitch information and the continuous pitch discrimination necessary for performing this pitch memory task.

Adolescent↗
PubMed2003

Gray matter differences between musicians and nonmusicians.

Musicians learn complex motor and auditory skills at an early age and practice these specialized skills extensively from childhood through their entire careers. Using a voxel-by-voxel morphometric technique, we found gray matter volume differences in motor as well as auditory and visuospatial brain regions comparing professional musicians (keyboard players) with matched amateur musicians and nonmusicians. These multiregional differences might represent structural adaptations in response to long-term skill learning and repetitive rehearsal of these skills. This is supported by finding a strong association between structural differences, musician status, and practice intensity as well as by a wealth of supporting animal data showing structural changes in response to long-term motor training.

Brain↗
PubMed2002

Processing of temporal information and the basal ganglia: new evidence from fMRI.

Temporal information processing is a fundamental brain function, which might include central timekeeping mechanisms independent of sensory modality. Psychopharmacological and patient studies suggest a crucial role of the basal ganglia in time estimation. In this study, functional magnetic resonance imaging (fMRI) was applied in 15 healthy right-handed male subjects performing an auditory time estimation task (duration discrimination of tone pairs in the range of 1,000-1,400 ms) and frequency discriminations (tone pairs differing in pitch, around 1,000 Hz) as an active control task. Task difficulty was constantly modulated by an adaptive algorithm (weighted up-down method) reacting on individual performance. Time estimation (vs rest condition) elicited a distinct pattern of cerebral activity, including the right medial and both left and right dorsolateral prefrontal cortices (DLPFC), thalamus, basal ganglia (caudate nucleus and putamen), left anterior cingulate cortex, and superior temporal auditory areas. Most activations showed lateralisation to the right hemisphere and were similar in the frequency discrimination task. Comparing time and frequency tasks, we isolated activation in the right putamen restricted to time estimation only. This result supports the notion of central processing of temporal information associated with basal ganglia activity. Temporal information processing in the brain might thus be a distributed process of interaction between modality-dependent sensory cortical function, the putamen (with a timing-specific function), and additional prefrontal cortical systems related to attention and memory. Further investigations are needed to delineate the differential contributions of the striatum and other areas to timing.

Acoustic Stimulation↗
PubMed2002

Transient activation of a somatosensory area in painful hallucinations shown by fMRI.

The disturbance of somatosensory perception and bodily experiences, including somatosensory hallucinations, are main features of the coenaesthesia sub-syndrome of schizophrenia. We used functional MRI to study a coenaesthesia patient with rapidly fluctuating painful somatosensory hallucinatory perceptions. Transient brain activations accompanying hallucinations were similar to the pattern elicited in a control experiment (non-painful tactile stimulation). However, an area in the medial parietal cortex, including parts of the precuneus and previously characterised as a supplementary sensory area, was activated significantly stronger during hallucinations than the control condition. This finding demonstrates elevated brain activity in a somatosensory area accompanying painful somatic hallucinations.

Brain Mapping↗
PubMed2002

Phonological processing in dyslexic children: a study combining functional imaging and event related potentials.

Difficulties in phonological processing are currently considered one of the major causes for dyslexia. Nine dyslexic children and eight control children were investigated using functional magnetic resonance imaging (fMRI) during non-oral reading of German words. All subjects silently read words and pronounceable non-words in an event related potentials (ERP) investigation, as well. The fMRI showed a significant difference in the activation in the left inferior frontal gyrus between the dyslexic and control groups, resulting from a hyperactivation in the dyslexics. The ERP scalp distribution showed a significant distinction between the two groups concerning the topographic difference for left frontal electrodes in a time window 250-600 ms after stimulus onset for non-word reading. Both the fMRI and the ERP results support differences in phonological processing between dyslexic and normal-reading children.

Child↗