Gabriel Hoffmann

YNIMG Journal 2026 Journal Article

Resting-state fMRI coherence is selectively diminished around 0.1 Hz in patients with unilateral carotid artery stenosis

• Sangcheon Choi
• Gabriel Hoffmann
• Sebastian Schneider
• Stephan Kaczmarz
• Xin Yu
• Christine Preibisch
• Christian Sorg

In the brain, vasomotor dynamics at infra-slow frequencies (∼0.1 Hz), driven by synchronized oscillations of smooth muscle cells in vessel walls, are thought to play a crucial role in regulating cerebral perfusion and underlie resting-state functional connectivity (FC), typically measured by correlated time courses of functional signals. In particular, rodent studies have demonstrated that vasomotor activity contributes to the coherence of blood oxygenation level dependent (BOLD) signal fluctuations. However, in humans, detecting this contribution non-invasively remains challenging due to the limited spatiotemporal sensitivity of functional magnetic resonance imaging (fMRI) to vasomotion. Given that prior studies have identified internal carotid artery stenosis (ICAS) as an informative conditional lesion model of vasomotor and hemodynamic impairments in humans, we investigated whether ICAS affects interhemispheric BOLD coherence at ∼0.1 Hz. Using a multi-modal fMRI framework integrating resting-state fMRI with quantitative mapping of cerebral blood volume, blood flow, oxygen metabolism, and BOLD time lag, we compared BOLD coherence between patients with asymptomatic unilateral ICAS and healthy controls. Frequency-specific analysis revealed significantly diminished inter-hemispheric BOLD coherence at ∼0.1 Hz across canonical resting-state networks in ICAS patients, while ultra-slow (<0.05 Hz) coherence remained largely preserved. This reduction was spatially widespread across brain networks and particularly pronounced in watershed areas, i.e., border zones between major vascular territories, associated with significantly increased lateralization of cerebral blood volume (p < 0.01). Notably, coherence-based FC patterns at ∼0.1 Hz were heterogeneous within watershed areas but homogeneous outside, suggesting an interplay between compensatory mechanisms and cerebrovascular impairment. Taken together, our findings demonstrate that ICAS induces subtle, frequency- and region-specific alterations in interhemispheric FC, consistent with a model in which impaired vasomotor activity and hemodynamic dysfunctions impact resting-state FC in the human brain.

IJCAI Conference 2007 Conference Paper

• David Stavens
• Gabriel Hoffmann
• Sebastian Thrun

The mobile robotics community has traditionally addressed motion planning and navigation in terms of steering decisions. However, selecting the best speed is also important -- beyond its relationship to stopping distance and lateral maneuverability. Consider a high-speed (35 mph) autonomous vehicle driving off-road through challenging desert terrain. The vehicle should drive slowly on terrain that poses substantial risk. However, it should not dawdle on safe terrain. In this paper we address one aspect of risk -- shock to the vehicle. We present an algorithm for trading-off shock and speed in real-time and without human intervention. The trade-off is optimized using supervised learning to match human driving. The learning process is essential due to the discontinuous and spatially correlated nature of the control problem -- classical techniques do not directly apply. We evaluate performance over hundreds of miles of autonomous driving, including performance during the 2005 DARPA Grand Challenge. This approach was the deciding factor in our vehicle's speed for nearly 20% of the DARPA competition -- more than any other constraint except the DARPA-imposed speed limits -- and resulted in the fastest finishing time.