Miriam Schwalm | Johannes Gutenberg-Universität Mainz (original) (raw)

Papers by Miriam Schwalm

Research paper thumbnail of Author response: Brain states govern the spatio-temporal dynamics of resting-state functional connectivity

Research paper thumbnail of Author response: Cortex-wide BOLD fMRI activity reflects locally-recorded slow oscillation-associated calcium waves

Research paper thumbnail of Brain states govern the spatio-temporal dynamics of resting state functional connectivity

Previously, using simultaneous task-free fMRI and optic-fiber-based neuronal calcium recordings i... more Previously, using simultaneous task-free fMRI and optic-fiber-based neuronal calcium recordings in the anesthetized rat, we identified BOLD responses directly related to slow calcium waves, revealing a cortex-wide and spatially organized BOLD correlate (Schwalm et al. 2017). Here, with these bimodal recordings, we reveal two distinct brain states: persistent state, in which compartmentalized network activity was observed, including defined subsets such as the default mode network; and slow wave state, dominated by a cortex-wide component, suggesting a strong functional coupling of brain activity. In slow wave state we find a correlation between slow wave events and the strength of functional connectivity. These findings suggest that indeed down-up transitions of neuronal excitability drive cortex-wide functional connectivity. This study provides strong evidence that previously reported changes in functional connectivity are highly dependent on the brain's current state and direc...

Research paper thumbnail of Back to Pupillometry: How Cortical Network State Fluctuations Tracked by Pupil Dynamics Could Explain Neural Signal Variability in Human Cognitive Neuroscience

eneuro

Significance Statement The mammalian thalamocortical system generates intrinsic activity reflecti... more Significance Statement The mammalian thalamocortical system generates intrinsic activity reflecting different states of excitability, arising from changes in the membrane potentials of underlying neuronal networks. Fluctuations between these states occur spontaneously, regularly, and frequently throughout awake periods and influence stimulus encoding, information processing, and neuronal and behavioral responses. Changes of pupil size have recently been identified as a reliable marker of underlying neuronal membrane potential and thus can encode associated network state changes in rodent cortex. This suggests that pupillometry, a ubiquitous measure of pupil dilation in cognitive neuroscience, could be used as an index for network state fluctuations also for human brain signals. Considering this variable may explain task-independent variance in neuronal and behavioral signals that were previously disregarded as noise.

Research paper thumbnail of Cortical temperature change - a tool for modulating brain states?

eNeuro, 2016

This commentary describes important findings of the article published by Sheroziya and Timofeev i... more This commentary describes important findings of the article published by Sheroziya and Timofeev in The Journal of Neuroscience in 2015. The authors use moderate cortical temperature change, local cooling or heating of somatosensory cortex, to modulate excitable states of the brain. These changes, under physiological conditions, result from neuromodulation, as well as other network effects. They report that cooling disrupts thalamocortical slow oscillations and induces an activated cortical state, while mild heating has the opposite effect and increases slow-wave rhythmicity. We evaluate these findings regarding their utility for inducing and investigating cortical state fluctuations, compare the results to physiologically occurring state changes, and put them into perspective with other discoveries in the field. Commentary

Research paper thumbnail of Assessing sensory versus optogenetic network activation by combining (o)fMRI with optical Ca 2+ recordings

Journal of Cerebral Blood Flow & Metabolism, 2015

Research paper thumbnail of Cortex-wide BOLD fMRI activity reflects locally-recorded slow oscillation-associated calcium waves

eLife

Spontaneous slow oscillation-associated slow wave activity represents an internally generated sta... more Spontaneous slow oscillation-associated slow wave activity represents an internally generated state which is characterized by alternations of network quiescence and stereotypical episodes of neuronal activity - slow wave events. However, it remains unclear which macroscopic signal is related to these active periods of the slow wave rhythm. We used optic fiber-based calcium recordings of local neural populations in cortex and thalamus to detect neurophysiologically defined slow calcium waves in isoflurane anesthetized rats. The individual slow wave events were used for an event-related analysis of simultaneously acquired whole-brain BOLD fMRI. We identified BOLD responses directly related to onsets of slow calcium waves, revealing a cortex-wide BOLD correlate: the entire cortex was engaged in this specific type of slow wave activity. These findings demonstrate a direct relation of defined neurophysiological events to a specific BOLD activity pattern and were confirmed for ongoing slo...

Research paper thumbnail of True and apparent optogenetic BOLDfMRI signals

Magnetic Resonance in Medicine, 2016

Optogenetic fMRI (ofMRI) is a novel tool in neurophysiology and neuroimaging. The method is prone... more Optogenetic fMRI (ofMRI) is a novel tool in neurophysiology and neuroimaging. The method is prone to light-induced artifacts, two of which were investigated in this study. ofMRI was performed in rats using two excitatory opsins (ChR2 and C1V1TT ) virally transduced in somatosensory cortex or thalamus. Heat-induced apparent BOLD activation at the site of the optical fiber and stimulation light-induced activation of the visual pathways were investigated, and control experiments for these two artifacts were established. Specific optogenetic BOLD activation was observed with both opsins, accompanied by BOLD in the visual pathways. Unspecific heat-induced BOLD was ruled out by a control experiment employing low-level constant illumination in addition to pulsed optogenetic stimulation. Activation of the visual pathways was confirmed to be physiological by direct visual stimulation of the eyes and was suppressed by additional low-level constant light to the eyes. Light inside the brain was identified as one source of the BOLD signal observed in the visual pathways. ofMRI is a method of tremendous potential, but unspecific activations in fMRI not caused by the activation of opsins must be avoided or recognized as such. The control experiments presented here allow for validating the specificity of optogenetic stimulation. Magn Reson Med, 2016. © 2016 Wiley Periodicals, Inc.

Research paper thumbnail of Brain areas involved in perception of motion in depth: a human fMRI study

Research paper thumbnail of Author response: Brain states govern the spatio-temporal dynamics of resting-state functional connectivity

Research paper thumbnail of Author response: Cortex-wide BOLD fMRI activity reflects locally-recorded slow oscillation-associated calcium waves

Research paper thumbnail of Brain states govern the spatio-temporal dynamics of resting state functional connectivity

Previously, using simultaneous task-free fMRI and optic-fiber-based neuronal calcium recordings i... more Previously, using simultaneous task-free fMRI and optic-fiber-based neuronal calcium recordings in the anesthetized rat, we identified BOLD responses directly related to slow calcium waves, revealing a cortex-wide and spatially organized BOLD correlate (Schwalm et al. 2017). Here, with these bimodal recordings, we reveal two distinct brain states: persistent state, in which compartmentalized network activity was observed, including defined subsets such as the default mode network; and slow wave state, dominated by a cortex-wide component, suggesting a strong functional coupling of brain activity. In slow wave state we find a correlation between slow wave events and the strength of functional connectivity. These findings suggest that indeed down-up transitions of neuronal excitability drive cortex-wide functional connectivity. This study provides strong evidence that previously reported changes in functional connectivity are highly dependent on the brain's current state and direc...

Research paper thumbnail of Back to Pupillometry: How Cortical Network State Fluctuations Tracked by Pupil Dynamics Could Explain Neural Signal Variability in Human Cognitive Neuroscience

eneuro

Significance Statement The mammalian thalamocortical system generates intrinsic activity reflecti... more Significance Statement The mammalian thalamocortical system generates intrinsic activity reflecting different states of excitability, arising from changes in the membrane potentials of underlying neuronal networks. Fluctuations between these states occur spontaneously, regularly, and frequently throughout awake periods and influence stimulus encoding, information processing, and neuronal and behavioral responses. Changes of pupil size have recently been identified as a reliable marker of underlying neuronal membrane potential and thus can encode associated network state changes in rodent cortex. This suggests that pupillometry, a ubiquitous measure of pupil dilation in cognitive neuroscience, could be used as an index for network state fluctuations also for human brain signals. Considering this variable may explain task-independent variance in neuronal and behavioral signals that were previously disregarded as noise.

Research paper thumbnail of Cortical temperature change - a tool for modulating brain states?

eNeuro, 2016

This commentary describes important findings of the article published by Sheroziya and Timofeev i... more This commentary describes important findings of the article published by Sheroziya and Timofeev in The Journal of Neuroscience in 2015. The authors use moderate cortical temperature change, local cooling or heating of somatosensory cortex, to modulate excitable states of the brain. These changes, under physiological conditions, result from neuromodulation, as well as other network effects. They report that cooling disrupts thalamocortical slow oscillations and induces an activated cortical state, while mild heating has the opposite effect and increases slow-wave rhythmicity. We evaluate these findings regarding their utility for inducing and investigating cortical state fluctuations, compare the results to physiologically occurring state changes, and put them into perspective with other discoveries in the field. Commentary

Research paper thumbnail of Assessing sensory versus optogenetic network activation by combining (o)fMRI with optical Ca 2+ recordings

Journal of Cerebral Blood Flow & Metabolism, 2015

Research paper thumbnail of Cortex-wide BOLD fMRI activity reflects locally-recorded slow oscillation-associated calcium waves

eLife

Spontaneous slow oscillation-associated slow wave activity represents an internally generated sta... more Spontaneous slow oscillation-associated slow wave activity represents an internally generated state which is characterized by alternations of network quiescence and stereotypical episodes of neuronal activity - slow wave events. However, it remains unclear which macroscopic signal is related to these active periods of the slow wave rhythm. We used optic fiber-based calcium recordings of local neural populations in cortex and thalamus to detect neurophysiologically defined slow calcium waves in isoflurane anesthetized rats. The individual slow wave events were used for an event-related analysis of simultaneously acquired whole-brain BOLD fMRI. We identified BOLD responses directly related to onsets of slow calcium waves, revealing a cortex-wide BOLD correlate: the entire cortex was engaged in this specific type of slow wave activity. These findings demonstrate a direct relation of defined neurophysiological events to a specific BOLD activity pattern and were confirmed for ongoing slo...

Research paper thumbnail of True and apparent optogenetic BOLDfMRI signals

Magnetic Resonance in Medicine, 2016

Optogenetic fMRI (ofMRI) is a novel tool in neurophysiology and neuroimaging. The method is prone... more Optogenetic fMRI (ofMRI) is a novel tool in neurophysiology and neuroimaging. The method is prone to light-induced artifacts, two of which were investigated in this study. ofMRI was performed in rats using two excitatory opsins (ChR2 and C1V1TT ) virally transduced in somatosensory cortex or thalamus. Heat-induced apparent BOLD activation at the site of the optical fiber and stimulation light-induced activation of the visual pathways were investigated, and control experiments for these two artifacts were established. Specific optogenetic BOLD activation was observed with both opsins, accompanied by BOLD in the visual pathways. Unspecific heat-induced BOLD was ruled out by a control experiment employing low-level constant illumination in addition to pulsed optogenetic stimulation. Activation of the visual pathways was confirmed to be physiological by direct visual stimulation of the eyes and was suppressed by additional low-level constant light to the eyes. Light inside the brain was identified as one source of the BOLD signal observed in the visual pathways. ofMRI is a method of tremendous potential, but unspecific activations in fMRI not caused by the activation of opsins must be avoided or recognized as such. The control experiments presented here allow for validating the specificity of optogenetic stimulation. Magn Reson Med, 2016. © 2016 Wiley Periodicals, Inc.

Research paper thumbnail of Brain areas involved in perception of motion in depth: a human fMRI study