Functional and diagnostic significance of the fMRI-response type to motor loads in patients after traumatic brain damage

Aim of the study. Clarification of the functional and diagnostic significance of topography, or the type of fMRI-response recorded during active and passive hand movements in patients after traumatic brain injury.Material and methods. fMRI-responses gained during active and passive hand movements were analyzed in 40 patients with posttraumatic motor function disturbances and compared with results gained from 17 healthy volunteers (control group ).Results. In analyzed patients the increase of percentage of diffuse fMRI-response has been shown along with the areas of activation not typical for movement activation pattern typical healthy volunteers. The fMRI response type being it local or multifocal does not clearly correlate with the presence of motor function impairment (hemiparesis). However, it was found that with greater severity of hemiparesis there is a larger percentage of multifocal fMRI-response.The transition from a multifocal form of a motor fMRI-response to a local one observed in a dynamic study is accompanied by an improvement of patient’s general condition, a shift towards normalization of a number of morphofunctional indicators of the central nervous system, the tendency of regression of motor disorders.Conclusion. The increase of multifocal fMRI-responses in patients after traumatic brain injury is one of the signs of cerebral dysfunction. Dynamically observed transformation from multifocal to local fMRI-responses is associated with current or long-term improvement in motor activity as well, wit the regression of other clinical impairments and can be considered as prognostically positive sign of the course of post-traumatic illness.

A quadratic model captures the human V1 response to variations in chromatic direction and contrast

An important goal for vision science is to develop quantitative models of the representation of visual signals at post-receptoral sites. To this end, we develop the quadratic color model (QCM) and examine its ability to account for the BOLD fMRI response in human V1 to spatially-uniform, temporal chromatic modulations that systematically vary in chromatic direction and contrast. We find that the QCM explains the same, cross-validated variance as a conventional general linear model, with far fewer free parameters. The QCM generalizes to allow prediction of V1 responses to a large range of modulations. We replicate the results for each subject and find good agreement across both replications and subjects. We find that within the LM cone contrast plane, V1 is most sensitive to L-M contrast modulations and least sensitive to L+M contrast modulations. Within V1, we observe little to no change in chromatic sensitivity as a function of eccentricity.

fMRI response to automatic and purposeful familiar-face processing in perceptual and nonperceptual cortical regions

Information is extracted from familiar faces in both automatic and active modes. Using functional MRI, we show: 1) that automatic access results in the selective activation of nonperceptual brain regions, the precuneus, ventromedial prefrontal cortex, and the anterior face patch and amygdala, demonstrating the automaticity of access to information in these regions; 2) selective increases in the activation of the lateral anterior temporal lobe and posterior superior temporal gyrus when biographic information is actively extracted.

A Quadratic Model Captures the Human V1 Response to Variations in Chromatic Direction and Contrast

An important goal for vision science is to develop quantitative models for the representation of visual signals at post-receptoral sites. To this end, we develop the quadratic color model (QCM) and examine its ability to account for the BOLD fMRI response in human V1 to spatially-uniform temporal chromatic modulations, systematically varying in their chromatic directions and contrasts. We find that the QCM explains the same, cross-validated variance as a conventional GLM, with far fewer free parameters. The QCM generalizes to allow prediction of V1 responses to a large range of modulations. We replicated the results for each subject and find good agreement across both replications and subjects. We find that within the LM cone contrast plane, V1 is most sensitive to L-M contrast modulations and least sensitive to L+M contrast modulations. Within V1, we observe little to no change in chromatic sensitivity as a function of eccentricity.

Characteristics of fMRI responses to visual stimulation in anesthetized vs. awake mice

The functional characteristics of the mouse visual system have not previously been well explored using fMRI. In this research, we examined 9.4 T BOLD fMRI responses to visual stimuli of varying pulse durations (1 – 50 ms) and temporal frequencies (1 – 10 Hz) under ketamine and xylazine anesthesia, and compared fMRI responses of anesthetized and awake mice. Under anesthesia, significant positive BOLD responses were detected bilaterally in the major structures of the visual pathways, including the dorsal lateral geniculate nuclei, superior colliculus, lateral posterior nucleus of thalamus, primary visual area, and higher-order visual area. BOLD responses increased slightly with pulse duration, were maximal at 3 – 5 Hz stimulation, and significantly decreased at 10 Hz, which were all consistent with previous neurophysiological findings. When the mice were awake, the BOLD fMRI response was faster in all active regions and stronger in the subcortical areas compared with the anesthesia condition. In the V1, the BOLD response was biphasic for 5 Hz stimulation and negative for 10 Hz stimulation under wakefulness, whereas prolonged positive BOLD responses were observed at both frequencies under anesthesia. Unexpected activation was detected in the extrastriate postrhinal area and non-visual subiculum complex under anesthesia, but not under wakefulness. Widespread positive BOLD activity under anesthesia likely results from the disinhibition and sensitization of excitatory neurons induced by ketamine. Overall, fMRI can be a viable tool for mapping brain-wide functional networks.

Bipartite Functional Fractionation within the Default Network Supports Disparate Forms of Internally Oriented Cognition

Our understanding about the functionality of the brain’s default network (DN) has significantly evolved over the past decade. Whereas traditional views define this network based on its suspension/disengagement during task-oriented behavior, contemporary accounts have characterized various situations wherein the DN actively contributes to task performance. However, it is unclear how different task-contexts drive componential regions of the DN to coalesce into a unitary network and fractionate into different subnetworks. Here we report a compendium of evidence that provides answers to these questions. Across multiple analyses, we found a striking dyadic structure within the DN in terms of the profiles of task-triggered fMRI response and effective connectivity, significantly extending beyond previous inferences based on meta-analysis and resting-state activities. In this dichotomy, one subset of DN regions prefers mental activities “interfacing with” perceptible events, while the other subset prefers activities “detached from” perceptible events. While both show a common “aversion” to sensory-motoric activities, their differential preferences manifest a subdivision that sheds light upon the taxonomy of the brain’s memory systems. This dichotomy is consistent with proposals of a macroscale gradational structure spanning across the cerebrum. This gradient increases its representational complexity, from primitive sensory-motoric processing, through lexical-semantic representations, to elaborated self-generated thoughts.