Conditional granger causality analysis of fMRI data shows a direct connection from LGN to hMT+ bypassing V1

The human middle temporal complex (hMT+) is devoted to motion perception. To determine whether motion-related neural information may reach hMT+ directly from the thalamus, by-passing the primary visual cortex (V1), we measured effective connectivity in an optic flow fMRI experiment in humans. Conditional Granger Causality analysis was employed to measure direct influences between the lateral geniculate nucleus (LGN) and hMT+, discarding indirect effects mediated by V1. Results indicated the existence of a bilateral alternative pathway for visual motion processing that allows for a direct flow of information from LGN to hMT+. This direct link may play a role in blindsight

It’s not all in your car: functional and structural correlates of exceptional driving skills in professional racers

Driving is a complex behavior that requires the integration of multiple cognitive functions. While many studies have investigated brain activity related to driving simulation under distinct conditions, little is known about the brain morphological and functional architecture in professional competitive driving, which requires exceptional motor and navigational skills. Here, 11 professional racing-car drivers and 11 “naïve” volunteers underwent both structural and functional brain magnetic resonance imaging (MRI) scans. Subjects were presented with short movies depicting a Formula One car racing in four different official circuits. Brain activity was assessed in terms of regional response, using an Inter-Subject Correlation (ISC) approach, and regional interactions by mean of functional connectivity. In addition, voxel-based morphometry (VBM) was used to identify specific structural differences between the two groups and potential interactions with functional differences detected by the ISC analysis. Relative to non-experienced drivers, professional drivers showed a more consistent recruitment of motor control and spatial navigation devoted areas, including premotor/motor cortex, striatum, anterior, and posterior cingulate cortex and retrosplenial cortex, precuneus, middle temporal cortex, and parahippocampus. Moreover, some of these brain regions, including the retrosplenial cortex, also had an increased gray matter density in professional car drivers. Furthermore, the retrosplenial cortex, which has been previously associated with the storage of observer-independent spatial maps, revealed a specific correlation with the individual driver's success in official competitions. These findings indicate that the brain functional and structural organization in highly trained racing-car drivers differs from that of subjects with an ordinary driving experience, suggesting that specific anatomo-functional changes may subtend the attainment of exceptional driving performance

It's not all in your car: functional and structural correlates of exceptional driving skills in professional racers.

Driving is a complex behavior that requires the integration of multiple cognitive functions. While many studies have investigated brain activity related to driving simulation under distinct conditions, little is known about the brain morphological and functional architecture in professional competitive driving, which requires exceptional motor and navigational skills. Here, 11 professional racing-car drivers and 11 "naïve" volunteers underwent both structural and functional brain magnetic resonance imaging (MRI) scans. Subjects were presented with short movies depicting a Formula One car racing in four different official circuits. Brain activity was assessed in terms of regional response, using an Inter-Subject Correlation (ISC) approach, and regional interactions by mean of functional connectivity. In addition, voxel-based morphometry (VBM) was used to identify specific structural differences between the two groups and potential interactions with functional differences detected by the ISC analysis. Relative to non-experienced drivers, professional drivers showed a more consistent recruitment of motor control and spatial navigation devoted areas, including premotor/motor cortex, striatum, anterior, and posterior cingulate cortex and retrosplenial cortex, precuneus, middle temporal cortex, and parahippocampus. Moreover, some of these brain regions, including the retrosplenial cortex, also had an increased gray matter density in professional car drivers. Furthermore, the retrosplenial cortex, which has been previously associated with the storage of observer-independent spatial maps, revealed a specific correlation with the individual driver's success in official competitions. These findings indicate that the brain functional and structural organization in highly trained racing-car drivers differs from that of subjects with an ordinary driving experience, suggesting that specific anatomo-functional changes may subtend the attainment of exceptional driving performance

How skill expertise shapes the brain functional architecture: an fMRI study of visuo-spatial and motor processing in professional racing-car and naïve drivers

The present study was designed to investigate the brain functional architecture that subserves visuo-spatial and motor processing in highly skilled individuals. By using functional magnetic resonance imaging (fMRI), we measured brain activity while eleven Formula racing-car drivers and eleven ‘naïve’ volunteers performed a motor reaction and a visuo-spatial task. Tasks were set at a relatively low level of difficulty such to ensure a similar performance in the two groups and thus avoid any potential confounding effects on brain activity due to discrepancies in task execution. The brain functional organization was analyzed in terms of regional brain response, inter-regional interactions and blood oxygen level dependent (BOLD) signal variability. While performance levels were equal in the two groups, as compared to naïve drivers, professional drivers showed a smaller volume recruitment of task-related regions, stronger connections among task-related areas, and an increased information integration as reflected by a higher signal temporal variability. In conclusion, our results demonstrate that, as compared to naïve subjects, the brain functional architecture sustaining visuo-motor processing in professional racing-car drivers, trained to perform at the highest levels under extremely demanding conditions, undergoes both ‘quantitative’ and ‘qualitative’ modifications that are evident even when the brain is engaged in relatively simple, non-demanding tasks. These results provide novel evidence in favor of an increased ‘neural efficiency’ in the brain of highly skilled individuals

Analysis of Blood Oxygenation Level Dependent (BOLD) signal to assess the temporal dynamics of visual motion perception in the human brain and its implication for functional Magnetic Resonance Imaging (fMRI)

Visual motion processing is one of the main subsystems of the visual system of primates, as the ability to perceive and detect motion is essential for survival in a complex environment. Speed and direction of motion in a complex visual scene are processed by the human middle temporal (MT) complex (hMT+), a region of the extrastriate cortex that plays a central role in visual motion perception. It is well known that the main pathway that conveys visual motion information from the retina to MT involves two main processing stages, one at the level of the thalamus, in the Lateral Geniculate Nucleus (LGN), and the other one in the primary visual cortex (V1) . However, anatomical studies in primates have suggested the existence of at least two other pathways that convey visual motion information from the thalamus straight to area MT, that is, without passing through V1. While all these findings may suggest a direct link from the thalamus to hMT+, a direct functional influence exerted by thalamic nuclei on hMT+ remained to be proven. We conducted functional fMRI experiments to record brain activity in response to moving visual stimuli. Performing CGC analysis on the BOLD fMRI time-series of LGN, hMT+ and V1, a significant direct influence of the BOLD signal recorded in LGN over that in hMT+, not mediated by V1 activity, was demonstrated, suggesting the co-existence of an alternative route that directly links LGN to hMT+. Moreover, it has been observed that hMT+ response latencies and amplitude vary as a function of speed, raising the question whether these characteristics reflect a property of the functional connection with LGN. Thus, we performed a new experiment to measure the causal influence between LGN and hMT+, in the presence of fast and slow visual stimuli in order to better understand the influence of speed on this direct connection. Computing differences between the strength of the causal connection from LGN to hMT+ in the two speed conditions, we detected two clusters of voxels in hMT+ whose connections with LGN are stronger in either the slow or the fast condition. In order to move our evidence of a direct connection between LGN and hMT+ based on the dynamics of BOLD signals towards a neuronal interpretation, more direct measurements of neural activity are needed. The neurovascular and neurometabolic coupling between blood flow supply and neural activity is still debated since the BOLD is an indirect effect of a combination of changes in Cerebral Blood Volume (CBV), Cerebral Blood Flow (CBF), and oxygen consumption (CMRO2) . Using dynamic responses of BOLD signal using Gradient Echo acquisition techniques, CBV (using superparamagnetic iron oxide), CBF (by arterial spin labeling and laser-Dopper flowmetry) and Temperature (using copper-constantan thermocouple wire), we characterized the coupling between these parameters across three transcortical segments along the vertical axis of the rat's primary somatosensory cortex during forepaw stimulation. Since BOLD, temperature and CMR02 modeling dynamics vary their relationship across each segment, layer-specific changes of these neurophysiologic, hemodynamic, and metabolic measurements are needed to better interpret high-resolution functional magnetic resonance imaging (fMRI) data. Combination of multi modal neuroimaging techniques and advanced analysis will substantially contribute to quantitatively relate the BOLD signal to changes in neurotransmission and electrical activity and will help to elucidate the neurophysiological processes of the human brain

Brain connectivity : study and implementation of methods to quantify directed influence in the brain based on fMRI data

Studio e implementazione di metodi per quantificare le influenze dirette a livello cerebrale. Valutazione delle prestazioni e delle differenze degli algoritmi di Granger Causality, Direct Transfer Function e Coherence ai fini di mappare la connettività funzionale e effettiva cerebrale

Exploring visual and auditory motion spatial frequencies computation in area hMT+

The hMT+ region of the brain has been established as being highly responsive to motion perception, particularly also in relation to specific features such as the spatial frequencies of visual stimuli. Moreover, recent studies have revealed that hMT+ is not solely involved in motion processing within the visual modality, but also exhibits activation in response to stimuli presented in the auditory modality. However, it remains unclear whether hMT+ demonstrates selectivity for spatial frequencies in this alternative sensory modality. To address this question, we conducted a functional magnetic resonance imaging (fMRI) experiment at an ultra-high magnetic field strength (7T), involving a cohort of 15 participants. During these sessions, participants were presented with visual and auditory stimuli, each involving translational motion, and were exposed to two distinct spatial frequencies (low and high). We use Multivariate Pattern Analyses (MVPA) allowing us to discern potential differences in hMT+ activation patterns between the two spatial frequency conditions across modalities. By employing these advanced neuroimaging techniques, our study endeavours to shed light on the potential selectivity of hMT+ for spatial frequencies also in a non-visual modality. Preliminary findings from the visual domain indicate that hMT+ indeed exhibits divergent activation patterns in response to the two spatial frequencies. To further investigate this phenomenon, we are currently exploring whether similar patterns can be observed in hMT+ when participants are subjected to auditory stimulation. Additionally, we aim to ascertain whether the spatial frequency pattern information is shared across the sensory modalities tested, utilizing cross-modal MVPA analyses

A Model of Transcytosis Processes Across the Blood Brain Barrier

Several problems that involves brain drug delivery depend on the possibility of blood brain barrier (BBB) crossing drug molecules properties. Transcytosis is an important way to cross BBB. In this study an analytic model is realized of this kind of transport process, that should be useful to help researcher activity, according to ethical problems that involve in vivo brain studies. The obtained model is a generalization of previous models of endocytosis extended to consider the esocytosis process at the apical side of BBB endothelial cell. A set of eight differential equations is obtained, that has been simplified according to biological hypotheses. The lack of experimental datasets make difficult an exact model validation. However, kinetic constants could be extrapolated from literature data. Thanks to this model, it should be possible to predict the concentration of the selected molecule in the brain, as a function of its concentration in the plasma. This paper reports on the model definition and its implementation in the Matlab Simulink environment

Evidence of a direct influence between the thalamus and hMT + independent of V1 in the human brain as measured by fMRI

In the present study we employed Conditional Granger Causality (CGC) and Coherence analysis to investigate whether visual motion-related information reaches the human middle temporal complex (hMT +) directly from the Lateral Geniculate Nucleus (LGN) of the thalamus, by-passing the primary visual cortex (V1). Ten healthy human volunteers underwent brain scan examinations by functional magnetic resonance imaging (fMRI) during two optic flow experiments. In addition to the classical LGN-V1-hMT + pathway, our results showed a significant direct influence of the blood oxygenation level dependent (BOLD) signal recorded in {LGN} over that in hMT+, not mediated by {V1} activity, which strongly supports the existence of a bilateral pathway that connects {LGN} directly to hMT + and serves visual motion processing. Furthermore, we evaluated the relative latencies among areas functionally connected in the processing of visual motion. Using {LGN} as a reference region, hMT + exhibited a statistically significant earlier peak of activation as compared to V1. In conclusion, our findings suggest the co-existence of an alternative route that directly links {LGN} to hMT+, bypassing V1. This direct pathway may play a significant functional role for the faster detection of motion and may contribute to explain persistence of unconscious motion detection in individuals with severe destruction of primary visual cortex (blindsight)

Correspondence between fMRI and electrophysiology during visual motion processing in human MT

Changes in brain neuronal activity are reflected by hemodynamic responses mapped through Blood Oxygenation Level Dependent (BOLD) functional magnetic resonance imaging (fMRI), a primary tool to measure brain functioning non-invasively. However, the exact relationship between hemodynamics and neuronal function is still a matter of debate. Here, we combine 3T BOLD fMRI and High Frequency Band (HFB) electrocorticography (ECoG) signals to investigate the relationship between neuronal activity and hemodynamic responses in the human Middle Temporal complex (hMT+), a higher order brain area involved in visual motion processing. We modulated the ECoG HFB and fMRI BOLD responses with a visual stimulus moving at different temporal frequencies, and compared measured BOLD responses to estimated BOLD responses that were predicted from the temporal profile of the HFB power change. We show that BOLD responses under an electrode over hMT+ can be well predicted not only be the strength of the neuronal response but also by the temporal profile of the HFB responses recorded by this electrode. Our results point to a linear relationship between BOLD and neuronal activity in hMT+, extending previous findings on primary cortex to higher order cortex