Context-dependent limb movement encoding in neuronal populations of motor cortex.

Neuronal networks of the mammalian motor cortex (M1) are important for dexterous control of limb joints. Yet it remains unclear how encoding of joint movement in M1 depends on varying environmental contexts. Using calcium imaging we measured neuronal activity in layer 2/3 of the M1 forelimb region while mice grasped regularly or irregularly spaced ladder rungs during locomotion. We found that population coding of forelimb joint movements is sparse and varies according to the flexibility demanded from individual joints in the regular and irregular context, even for equivalent grasping actions across conditions. This context-dependence of M1 encoding emerged during task learning, fostering higher precision of grasping actions, but broke apart upon silencing of projections from secondary motor cortex (M2). These findings suggest that M1 exploits information from M2 to adapt encoding of joint movements to the flexibility demands of distinct familiar contexts, thereby increasing the accuracy of motor output.

Spatially segregated feedforward and feedback neurons support differential odor processing in the lateral entorhinal cortex.

The lateral entorhinal cortex (LEC) computes and transfers olfactory information from the olfactory bulb to the hippocampus. Here we established LEC connectivity to upstream and downstream brain regions to understand how the LEC processes olfactory information. We report that, in layer II (LII), reelin- and calbindin-positive (RE(+) and CB(+)) neurons constitute two major excitatory cell types that are electrophysiologically distinct and differentially connected. RE(+) neurons convey information to the hippocampus, while CB(+) neurons project to the olfactory cortex and the olfactory bulb. In vivo calcium imaging revealed that RE(+) neurons responded with higher selectivity to specific odors than CB(+) neurons and GABAergic neurons. At the population level, odor discrimination was significantly better for RE(+) than CB(+) neurons, and was lowest for GABAergic neurons. Thus, we identified in LII of the LEC anatomically and functionally distinct neuronal subpopulations that engage differentially in feedforward and feedback signaling during odor processing.

Specific Early and Late Oddball-Evoked Responses in Excitatory and Inhibitory Neurons of Mouse Auditory Cortex.

A major challenge for sensory processing in the brain is considering stimulus context, such as stimulus probability, which may be relevant for survival. Excitatory neurons in auditory cortex, for example, adapt to repetitive tones in a stimulus-specific manner without fully generalizing to a low-probability deviant tone ("oddball") that breaks the preceding regularity. Whether such stimulus-specific adaptation (SSA) also prevails in inhibitory neurons and how it might relate to deviance detection remains elusive. We obtained whole-cell recordings from excitatory neurons and somatostatin- and parvalbumin-positive GABAergic interneurons in layer 2/3 of mouse auditory cortex and measured tone-evoked membrane potential responses. All cell types displayed SSA of fast ("early") subthreshold and suprathreshold responses with oddball tones of a deviant frequency eliciting enlarged responses compared with adapted standards. SSA was especially strong when oddball frequency matched neuronal preference. In addition, we identified a slower "late" response component (200-400 ms after tone onset), most clearly in excitatory and parvalbumin-positive neurons, which also displayed SSA. For excitatory neurons, this late component reflected genuine deviance detection. Moreover, intracellular blockade of NMDA receptors reduced early and late responses in excitatory but not parvalbumin-positive neurons. The late component in excitatory neurons thus shares time course, deviance detection, and pharmacological features with the deviant-evoked event-related potential known as mismatch negativity (MMN) and provides a potential link between neuronal SSA and MMN. In summary, our results suggest a two-phase cortical activation upon oddball stimulation, with oddball tones first reactivating the adapted auditory cortex circuitry and subsequently triggering delayed reverberating network activity. Significance statement: Understanding how the brain encodes sensory context in addition to stimulus feature has been a main focus in neuroscience. Using in vivo targeted whole-cell recordings from excitatory and inhibitory neurons of mouse primary auditory cortex, we report two temporally distinct components of membrane potential responses encoding oddball tones that break stimulus regularity. Both components display stimulus-specific adaptation upon oddball paradigm stimulation in the three recorded cell types. The late response component, in particular, carries signatures of genuine deviance detection. In excitatory but not parvalbumin-positive inhibitory neurons, both early and late components depend on NMDA receptor-signaling. Our work proposes a potential neuronal substrate of a known deviant-evoked event-related potential, which is of fundamental significance in basic and clinical neuroscience.

Microcircuit dynamics of map plasticity in barrel cortex.

Functional reorganization of the whisker map in rodent barrel cortex has long served as a model for cortical plasticity following changes in sensory experience. Given the heterogeneity of neuronal response properties in neocortex, it has remained unclear how individual neurons in the cortical microcircuit are affected. Novel in vivo imaging and electrophysiology methods allow longitudinal recording of the same neurons' functional properties and therefore have the critical ability to resolve the direction and dynamics of change as plasticity progresses. Tracking sensory responsiveness before and after whisker trimming has uncovered diverse effects in individual neurons, suggesting that longitudinal recording will be essential for elucidating plasticity mechanisms within cortical microcircuits.

Neurofeedback of slow cortical potentials: neural mechanisms and feasibility of a placebo-controlled design in healthy adults.

To elucidate basic mechanisms underlying neurofeedback we investigated neural mechanisms of training of slow cortical potentials (SCPs) by considering EEG- and fMRI. Additionally, we analyzed the feasibility of a double-blind, placebo-controlled design in NF research based on regulation performance during treatment sessions and self-assessment of the participants. Twenty healthy adults participated in 16 sessions of SCPs training: 9 participants received regular SCP training, 11 participants received sham feedback. At three time points (pre, intermediate, post) fMRI and EEG/ERP-measurements were conducted during a continuous performance test (CPT). Performance-data during the sessions (regulation performance) in the treatment group and the placebo group were analyzed. Analysis of EEG-activity revealed in the SCP group a strong enhancement of the CNV (electrode Cz) at the intermediate assessment, followed by a decrease back to baseline at the post-treatment assessment. In contrast, in the placebo group a continuous but smaller increase of the CNV could be obtained from pre to post assessment. The increase of the CNV in the SCP group at intermediate testing was superior to the enhancement in the placebo group. The changes of the CNV were accompanied by a continuous improvement in the test performance of the CPT from pre to intermediate to post assessment comparable in both groups. The change of the CNV in the SCP group is interpreted as an indicator of neural plasticity and efficiency while an increase of the CNV in the placebo group might reflect learning and improved timing due to the frequent task repetition. In the fMRI analysis evidence was obtained for neuronal plasticity. After regular SCP neurofeedback activation in the posterior parietal cortex decreased from the pre- to the intermediate measurement and increased again in the post measurement, inversely following the U-shaped increase and decrease of the tCNV EEG amplitude in the SCP-trained group. Furthermore, we found a localized increase of activity in the anterior cingulate cortex (ACC). Analyses of the estimation of treatment assignment by the participants indicate feasibility of blinding. Participants could not assess treatment assignment confidently. Participants of the SCP-group improved regulation capability during treatment sessions (in contrast to the participants of the placebo-group), although regulation capability appeared to be instable, presumably due to diminished confidence in the training (SCP- or sham-training). Our results indicate that SCP training in healthy adults might lead to functional changes in neuronal circuits serving cognitive preparation even after a limited number of sessions.

Steady or changing? Long-term monitoring of neuronal population activity.

Stability and flexibility are both hallmarks of brain function that allow animals to thrive in ever-changing environments. Investigating how a balance between these opposing features is achieved with a dynamic array of cellular and molecular constituents requires long-term tracking of activity from individual neurons. Here, we review in vivo chronic extracellular recording studies and recent long-term two-photon calcium-imaging investigations that address the question of stability and plasticity of neuronal population activity in the mammalian brain. Overall, spiking activity is heterogeneously distributed among neurons in local populations and largely remains stable for individual cells over time. Tuning properties appear more flexible and may be adaptively stabilized, possibly by neuromodulators, to encode reliably and specifically salient stimuli or behaviors.

Inference of neuronal network spike dynamics and topology from calcium imaging data.

Two-photon calcium imaging enables functional analysis of neuronal circuits by inferring action potential (AP) occurrence ("spike trains") from cellular fluorescence signals. It remains unclear how experimental parameters such as signal-to-noise ratio (SNR) and acquisition rate affect spike inference and whether additional information about network structure can be extracted. Here we present a simulation framework for quantitatively assessing how well spike dynamics and network topology can be inferred from noisy calcium imaging data. For simulated AP-evoked calcium transients in neocortical pyramidal cells, we analyzed the quality of spike inference as a function of SNR and data acquisition rate using a recently introduced peeling algorithm. Given experimentally attainable values of SNR and acquisition rate, neural spike trains could be reconstructed accurately and with up to millisecond precision. We then applied statistical neuronal network models to explore how remaining uncertainties in spike inference affect estimates of network connectivity and topological features of network organization. We define the experimental conditions suitable for inferring whether the network has a scale-free structure and determine how well hub neurons can be identified. Our findings provide a benchmark for future calcium imaging studies that aim to reliably infer neuronal network properties.

Reorganization of cortical population activity imaged throughout long-term sensory deprivation.

Sensory maps are reshaped by experience. It is unknown how map plasticity occurs in vivo in functionally diverse neuronal populations because activity of the same cells has not been tracked over long time periods. Here we used repeated two-photon imaging of a genetic calcium indicator to measure whisker-evoked responsiveness of the same layer 2/3 neurons in adult mouse barrel cortex over weeks, first with whiskers intact, then during continued trimming of all but one whisker. Across the baseline period, neurons displayed heterogeneous yet stable responsiveness. During sensory deprivation, responses to trimmed whisker stimulation globally decreased, whereas responses to spared whisker stimulation increased for the least active neurons and decreased for the most active neurons. These findings suggest that recruitment of inactive, 'silent' neurons is part of a convergent redistribution of population activity underlying sensory map plasticity. Sensory-driven responsiveness is a key property controlling experience-dependent activity changes in individual neurons.

Optical recording of neuronal activity with a genetically-encoded calcium indicator in anesthetized and freely moving mice.

Fluorescent calcium (Ca(2+)) indicator proteins (FCIPs) are promising tools for functional imaging of cellular activity in living animals. However, they have still not reached their full potential for in vivo imaging of neuronal activity due to limitations in expression levels, dynamic range, and sensitivity for reporting action potentials. Here, we report that viral expression of the ratiometric Ca(2+) sensor yellow cameleon 3.60 (YC3.60) in pyramidal neurons of mouse barrel cortex enables in vivo measurement of neuronal activity with high dynamic range and sensitivity across multiple spatial scales. By combining juxtacellular recordings and two-photon imaging in vitro and in vivo, we demonstrate that YC3.60 can resolve single action potential (AP)-evoked Ca(2+) transients and reliably reports bursts of APs with negligible saturation. Spontaneous and whisker-evoked Ca(2+) transients were detected in individual apical dendrites and somata as well as in local neuronal populations. Moreover, bulk measurements using wide-field imaging or fiber-optics revealed sensory-evoked YC3.60 signals in large areas of the barrel field. Fiber-optic recordings in particular enabled measurements in awake, freely moving mice and revealed complex Ca(2+) dynamics, possibly reflecting different behavior-related brain states. Viral expression of YC3.60 - in combination with various optical techniques - thus opens a multitude of opportunities for functional studies of the neural basis of animal behavior, from dendrites to the levels of local and large-scale neuronal populations.

Brain networks involved in early versus late response anticipation and their relation to conflict processing.

Previous electrophysiological studies have clearly identified separable neural events underlying early and late components of response anticipation. Functional neuroimaging studies, however, have so far failed to account for this separation. Here, we performed functional magnetic resonance imaging (fMRI) of an anticipation paradigm in 12 healthy adult subjects that reliably produced early and late expectancy waves in the electroencephalogram. We furthermore compared fMRI activations elicited during early and late anticipation to those associated with response conflict. Our results demonstrate the existence of distinct cortical and subcortical brain regions underlying early and late anticipation. Although late anticipatory behavior was associated with activations in dorsal ACC, frontal cortex, and thalamus, brain responses linked to the early expectancy wave were localized mainly in motor and premotor cortical areas as well as the caudate nucleus. Additionally, late anticipation was associated with increased activity in midbrain dopaminergic nuclei, very likely corresponding to the substantia nigra. Furthermore, whereas regions involved in late anticipation proved to be very similar to activations elicited by response conflict, this was not the case for early anticipation. The current study supports a distinction between early and late anticipatory processes, in line with a plethora of neurophysiological work, and for the first time describes the brain structures differentially involved in these processes.

Lateralized anterior cingulate function during error processing and conflict monitoring as revealed by high-resolution fMRI.

Recent studies have reported that functional subdivisions of anterior cingulate cortex (ACC) may be selectively responsible for conflict and error-related processing. We examined this claim by imaging ACC activation to correct and erroneous response inhibitions in a GoNogo task. After localizing the ACC cluster in individual subjects using functional magnetic resonance imaging (fMRI) at standard resolution (2 x 2 x 4 mm(3)), high-resolution fMRI (1.5 x 1.5 x 1.5 mm(3)) of the ACC was performed in a second session to investigate its precise functional anatomy. At standard resolution, and in agreement with previous studies, ACC was activated for correct and incorrect responses, albeit more so for errors. High-resolution maps of activated ACC clusters revealed localized and reproducible foci in 9 out of 10 volunteers. Multisubject analysis suggested a bilateral distribution of error-related processes in ACC, whereas correct inhibitions only seemed to activate ACC in the right hemisphere. Subsequent region of interest analysis largely confirmed the activation maps. Our results contribute toward a better understanding of the microanatomy of ACC and demonstrate the potential of fMRI for mapping the functional architecture of brain regions involved in cognitive tasks at a previously unaccomplished spatial scale.

The cost of parallel imaging in functional MRI of the human brain.

While the advantages of parallel acquisition techniques for echo-planar imaging (EPI) are well documented for studies affected by magnetic field inhomogeneities, this work focuses on the costs in functional MRI of brain regions without artifacts due to susceptibility effects. For a visual stimulation paradigm and relative to conventional EPI (2.9 T; TR/TE=2000/36 ms), the use of parallel acquisition at a reduction factor of 2 decreased the mean number of activated voxels by 21% at 2 x 2 x 2-mm(3) resolution (n=6) and by 15% at 3 x 3 x 3-mm(3) resolution (n=6). The loss of sensitivity reflects both a decreased signal-to-noise ratio of the native images due to a lower number of contributing gradient echoes and a decreased BOLD MRI sensitivity due to the coverage of a smaller range of TEs.

Effects of ethanol on kinaesthetic perception.

In normal subjects, alcohol increases handwriting size, but the mechanism is not understood. Here we show that the alcohol effect on handwriting can be explained by a selective impairment of kinaesthetic perception. Thirty volunteers (15 male, aged 18-29 years) took part in an open study. They were tested before and after a drink containing vodka intended to produce a blood alcohol concentration of about 80mg/100ml. Tests included kinaesthetic distance estimation, in which volunteers worked with preferred hand and arm behind a screen which hid their movements; visual distance estimation; and measures of handwriting and drawing. Blood alcohol concentration at 55min, based on breathalyser measurements, was 76.7mg/100ml (SD 9.8). When asked to move the hand and mark a distance of 10cm from a starting point, distances estimates increased by 7-10% (p 0.01). Similar increases were seen for writing words and drawing characters. Signatures were increased in height but not in length. Distances estimated visually were increased much less, by 3-4% (p 0.05). Tests of psychomotor performance indicated the expected effects of ethanol. These results suggest that ethanol affects writing size by reducing kinaesthetically perceived distances.