Biology subjects

Fries, P.

Publications and source records attributed to Fries, P..

7 recordsLinked to original sources

bioRxiv2018

Surface color and predictability determine contextual modulation of V1 firing and gamma oscillations

The integration of direct bottom-up inputs with contextual information is a canonical motif in neocortical circuits. In area V1, neurons may reduce their firing rates when the (classical) receptive field input can be predicted by the spatial context. We previously hypothesized that gamma-synchronization (30-80Hz) provides a complementary signal to rates, encoding whether stimuli are predicted from spatial context by preferentially synchronizing neuronal populations receiving predictable inputs. Here we investigated how rates and synchrony are modulated by predictive context. Large uniform surfaces, which have high spatial predictability, strongly suppressed firing yet induced prominent gamma-synchronization, but only when they were colored. Yet, chromatic mismatches between center and surround, breaking predictability, strongly reduced gamma-synchronization while increasing firing rates. Differences between colors, including strong gamma-responses to red, arose because of stimulus adaptation to a full-screen background, with a prominent difference in adaptation between M- and L-cone signaling pathways. Thus, synchrony signals whether RF inputs are predicted from spatial context and may encode relationships across space, while firing rates increase when stimuli are unpredicted from the context.

neuroscience↗

bioRxiv2018

Cortico-basal-ganglia communication: Temporally structured activity for selective motor control

Despite the hard-wired structural connectivity of neural pathways, neural circuits allow context-dependent reactions to sensory cues by triggering the desired movement. Cortico-basal-ganglia circuits seem particularly important for flexible motor control as this is impaired in Parkinsons disease (PD). We analysed subthalamic nucleus (STN) spike and cortical ECoG activity from PD patients performing a visually-cued hand grip task. Fast reaction times were preceded by enhanced STN spike-to-cortical gamma phase coupling irrespective of firing rate changes, suggesting a role of gamma coupling in motor preparation. STN spike timing was offset by half a cycle when comparing ipsilateral with contralateral movements. Additionally, cortical high-frequency activity increased more steeply within each gamma cycle at the sites that showed the strongest coupling with STN spikes. Cortico-basal-ganglia gamma coupling may thus help shape neural activity to facilitate selective motor control. The observation that this effect occurs independent of changes in mean firing rate has far-reaching implications.\n\nHighlightsO_LIFast RTs were preceded by enhanced STN spike-to-cortical gamma phase coupling\nC_LIO_LISTN spike probability was significantly modulated relative to the gamma cycle\nC_LIO_LIDuring ipsilateral movement, spikes were more likely at the opposite part of the cycle\nC_LIO_LISTN output may thus help shape cortical gamma for selective motor control\nC_LI

neuroscience↗

bioRxiv2018

Gamma synchronization between V1 and V4 improves behavioral performance

Motor behavior is often driven by visual stimuli, relying on efficient feedforward communication from lower to higher visual areas. The Communication-through-Coherence hypothesis proposes that interareal communication depends on coherence at an optimal phase relation. While previous studies have linked effective communication to enhanced interareal coherence, it remains unclear, whether this interareal coherence occurs at an optimal phase relation that actually improves the stimulus transmission to behavioral report. We recorded local field potentials simultaneously from areas V1 and V4 of macaque monkeys performing a selective visual attention task, during which they reported changes of the attended stimulus. Gamma synchronization between V1 and V4, immediately preceding the stimulus change, predicted subsequent reaction times (RTs). Crucially, RTs were systematically slowed as trial-by-trial interareal gamma phase relations deviated from the phase relation at which V1 and V4 synchronized on average. These effects were specific to the attended stimulus and not due to local power or phase inside V1 or V4. We conclude that interareal gamma synchronization occurs at the optimal phase relation and thereby improves interareal communication and the effective transformation of sensory inputs into motor responses.

neuroscience↗

bioRxiv2017

Reconstruction of resting-state networks from macaqueelectrocorticographic data

The discovery of haemodynamic (BOLD-fMRI) resting-state networks (RSNs) has brought about a fundamental shift in our thinking about the role of intrinsic brain activity. The electrophysiological underpinnings of RSNs remain largely elusive and it has been shown only recently that electrophysiological cortical rhythms are organized into RSNs. Most electrophysiological studies into RSNs use magnetoencephalography (MEG) or electroencephalography (EEG), which limits the spatial scale on which RSNs can be investigated. Due to their close proximity to the cortical surface, electroencephalographic (ECoG) recordings can potentially provide a more detailed picture of the functional organization of resting-state cortical rhythms. In this study we propose using source-space independent component analysis for identifying generators of resting-state cortical rhythms as recorded with ECoG and reconstructing their network structure. Their network structure is characterized by two kinds of connectivity: instantaneous correlations between band-limited amplitude envelopes and oscillatory phase-locking. Using simulated data, we find that the reconstruction of oscillatory phase-locking is more challenging than that of amplitude correlations, particularly for low signal-to-noise levels. Specifically, phase-lags can both be over- and underestimated as a consequence of first-order and higher-order volume-conduction effects, which troubles the interpretation of interaction measures based on imaginary phase-locking or coherence. The methodology is applied to resting-state beta (15-30 Hz) rhythms within the motor system of a macaque monkey and leads to the identification of a functional network of seven cortical generators that are distributed across the sensorimotor system. The spatial extent of the identified generators, together with consistent phase-lags, suggests that these rhythms can be viewed as being spatially continuous with complex dynamics including traveling waves. Our findings illustrate the level of spatial detail attainable with source-projected ECoG and motivates wider use of the methodology for studying resting-state as well as event-related cortical dynamics in macaque and human.

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bioRxiv2017

Gamma-Band Resonance Of Visual Cortex To Optogenetic Stimulation

Activated visual cortex typically engages in neuronal synchronization in the gamma-frequency band (30-90 Hz). Gamma-band synchronization is related to cognitive functioning, and its mechanisms have been extensively investigated, predominantly through in-vitro studies. To further elucidate its mechanisms in-vivo, we performed simultaneous optogenetic stimulation and electrophysiological recordings of visual cortical areas 17 and 21a in the anesthetized cat. Viral transfection with AAV1 or AAV9 under a CamKII promoter led to robust Channelrhodopsin-2 (ChR2) expression. Immunohistochemical analysis showed that all ChR2-expressing neurons were negative for Parvalbumin, consistent with predominant or exclusive expression in excitatory neurons. Optogenetic stimulation used primarily surface illumination directly above the transfected and recorded cells. Stimulation with constant light led to strong and sustained gamma-band synchronization with strength and bandwidth similar to visually induced gamma. Rhythmic stimulation with light-pulse trains or sinusoidal light modulation revealed strongest resonance for gamma-band frequencies. Gamma resonance was confirmed by optogenetic white-noise stimulation. White-noise stimulation allowed the quantification of the transfer function between the optogenetic stimulation and the local field potential response. This transfer function showed a dominant peak in the gamma band. Thus, we find that visual cortical circuits resonate most strongly to gamma-band components in their input. This resonance renders both the sensitivity to input, and the output of these circuits, selectively tuned to gamma.\n\nSignificance StatementActivated groups of cortical neurons often display rhythmic synchronization in the gamma-frequency band (30-90 Hz). Gamma-band synchronization is particularly well studied in visual cortex. We used optogenetics to control visual cortex neurons with light. Different optogenetic stimulation protocols, using constant light, rhythmically modulated light or white-noise modulated light, all demonstrated that the investigated circuits predominantly resonate to stimulation in the gamma band. The observed gamma-band resonance renders visual cortical circuits most sensitive to gamma-rhythmic synaptic inputs. This in turn renders their spike output and the ensuing interareal synchronization gamma rhythmic.\n\nThis work was supported by DFG (SPP 1665, FOR 1847, FR2557/5-1-CORNET to P.F.; EXC 1086, DI 1908/5-1, DI 1908/6-1 to I.D.), BMBF (01GQ1301 to I.D.), EU (HEALTH-F2-2008-200728-BrainSynch, FP7-604102-HBP, FP7-600730-Magnetrodes to P.F.; ERC Starting Grant OptoMotorPath to I.D.), a European Young Investigator Award to P.F., the FENS-Kavli Network of Excellence to I.D., National Institutes of Health (1U54MH091657-WU-Minn-Consortium-HCP to P.F.), the LOEWE program (NeFF to P.F. and I.D.). Present address of I.D.: Optophysiology, Bernstein Center and BrainLinks-BrainTools, University of Freiburg, Albertstrase 23, 79104 Freiburg, Germany.\n\nAuthor contributionsJ.N, C.M.L., T.W., P.F. designed research; J.N, C.M.L., T.W., P.J., I.D., P.F. performed experiments; J.N., C.M.L., T.W. analyzed data; J.N., P.F. wrote the paper.

neuroscience↗

bioRxiv2017

A Theta Rhythm In Awake Macaque V1 And V4 And Its Attentional Modulation

Theta rhythms govern rodent sniffing and whisking, and human language processing. Human psychophysics suggests a role for theta also in visual attention. Yet, little is known about theta in visual areas and its attentional modulation. We used electrocorticography (ECoG) to record local field potentials (LFPs) simultaneously from areas V1, V2, V4 and TEO of two macaque monkeys performing a selective visual attention task. We found a {approx}4 Hz theta rhythm within both the V1-V2 and the V4-TEO region, and theta synchronization between them, with a predominantly feedforward directed influence. ECoG coverage of large parts of these regions revealed a surprising spatial correspondence between theta and visually induced gamma. Furthermore, gamma power was modulated with theta phase. Selective attention to the respective visual stimulus strongly reduced these theta-rhythmic processes, leading to an unusually strong attention effect for V1. Microsaccades (MSs) were partly locked to theta. Yet, neuronal theta rhythms tended to be even more pronounced for epochs devoid of MSs. Thus, we find an MS-independent theta rhythm specific to visually driven parts of V1-V2, which rhythmically modulates local gamma and entrains V4-TEO, and which is strongly reduced by attention. We propose that the less theta-rhythmic and thereby more continuous processing of the attended stimulus serves the exploitation of this behaviorally most relevant information. The theta-rhythmic and thereby intermittent processing of the unattended stimulus likely reflects the ecologically important exploration of less relevant sources of information.

neuroscience↗

bioRxiv2016

In vivo magnetic recording of neuronal activity

Neuronal activity generates ionic flows and thereby both magnetic fields and electric potential differences, i.e. voltages. Voltage measurements are widely used, but suffer from isolating and smearing properties of tissue between source and sensor, are blind to ionic flow direction, and reflect the difference between two electrodes, complicating interpretation. Magnetic field measurements could overcome these limitations, but have been essentially limited to magnetoencephalography (MEG), using centimeter-sized, helium-cooled extracranial sensors. Here, we report on in vivo magnetic recordings of neuronal activity from visual cortex of cats with magnetrodes, specially developed needle-shaped probes carrying micron-sized, non-cooled magnetic sensors based on spin electronics. Event-related magnetic fields inside the neuropil were on the order of several nanoteslas, informing MEG source models and efforts for magnetic field measurements through MRI. Though the signal-to-noise ratio is still inferior to electrophysiology, this proof of concept demonstrates the potential to exploit the fundamental advantages of magnetophysiology.\n\nHIGHLIGHTSO_LISpin-electronics based probes achieve local magnetic recordings inside the neuropil\nC_LIO_LIMagnetic field recordings were performed in vivo, in anesthetized cat visual cortex\nC_LIO_LIEvent-related fields (ERFs) to visual stimuli were up to several nanoteslas in size\nC_LIO_LIERFs could be detected after averaging less than 20 trials\nC_LI\n\nIN BRIEFCaruso et al. report in vivo, intra-cortical recordings of magnetic fields that reflect neuronal activity, using magnetrodes, i.e. micron size magnetic sensors based on spin electronics.

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