Biology subjects

Rafeh, R. W.

Publications and source records attributed to Rafeh, R. W..

3 recordsLinked to original sources

bioRxiv2025

Multiplexed BOLD oscillations reveal the interplay of normalization and attention

Monkey electrophysiology has linked attention to divisive normalization, yet noninvasive evidence in humans remains limited. We use frequency-tagged fMRI to isolate visual cortical populations that simultaneously encode multiple competing inputs. We show that responses of these sites are suppressed during inattention and enhanced during attention - consistent with the normalization model, which predicts that attention selectively disinhibits competing inputs - offering a noninvasive translational bridge to study fine-grained computations underlying attentional selection.

neuroscience↗

bioRxiv2025

Attentional enhancement and suppression of stimulus-synchronized BOLD oscillations

Visual cortical neurons synchronize their firing rates to periodic visual stimuli. EEG is commonly used to study directed attention by frequency-tagging brain responses to multiple stimuli oscillating at different frequencies, but is limited by its coarse spatial resolution. Here we leverage frequency-tagging fMRI (ft-fMRI) to study the influence of directed attention on the fine-grained spatiotemporal dynamics of competing stimulus-driven visual cortical oscillations. Our analysis reveals that distinct populations of visual cortical neurons exhibit in-phase (enhancing) or anti-phase (suppressive) synchronization with the oscillating stimuli. Directed attention homogeneously increases the amplitude of anti-phase BOLD oscillations across the visual hierarchy, consistent with a distributed suppressive field. In contrast, attentional modulation of in-phase BOLD oscillations increases hierarchically from V1 to hV4. The strength of anti-phase, but not in-phase, modulation predicted psychophysical correlates of attentional performance. Our results strongly corroborate the biased competition model of attention and unveil a novel BOLD correlate of attentional suppression.

neuroscience↗

bioRxiv2024

Frequency-tagged fMRI: A platform for fine-grained spatiotemporal analysis of cortical function

Frequency tagging with functional MRI (ft-fMRI) enables precise mapping of neural dynamics by synchronizing oscillatory stimuli to stimulus-driven blood-oxygen-level-dependent (BOLD) responses. We developed and validated a dual-frequency tagging protocol to dissociate fundamental, multiplexed, and nonlinear intermodulation frequency responses across the human visual cortex at high spatial resolution. Using 3T and 7T fMRI, we reliably detected frequency-tagged BOLD responses at the level of individual vertices, revealing fine-grained cortical topographies and robust temporal synchronization to driving frequencies. Multiplexed responses, encoding multiple frequencies simultaneously, and nonlinear intermodulation components, were spatially dissociable and exhibited reproducible dynamics within and across experimental sessions. These findings establish ft-fMRI as a powerful tool for investigating fine-grained cortical computations, previously inaccessible to traditional fMRI. By bridging the spatiotemporal resolution gap between electrophysiology and fMRI, ft-fMRI provides a versatile platform for studying perception, attention, and multisensory integration in health and disease.

neuroscience↗