96 research outputs found
Olfactory learning alters navigation strategies and behavioral variability in C. elegans
Animals adjust their behavioral response to sensory input adaptively
depending on past experiences. The flexible brain computation is crucial for
survival and is of great interest in neuroscience. The nematode C. elegans
modulates its navigation behavior depending on the association of odor butanone
with food (appetitive training) or starvation (aversive training), and will
then climb up the butanone gradient or ignore it, respectively. However, the
exact change in navigation strategy in response to learning is still unknown.
Here we study the learned odor navigation in worms by combining precise
experimental measurement and a novel descriptive model of navigation. Our model
consists of two known navigation strategies in worms: biased random walk and
weathervaning. We infer weights on these strategies by applying the model to
worm navigation trajectories and the exact odor concentration it experiences.
Compared to naive worms, appetitive trained worms up-regulate the biased random
walk strategy, and aversive trained worms down-regulate the weathervaning
strategy. The statistical model provides prediction with accuracy of
the past training condition given navigation data, which outperforms the
classical chemotaxis metric. We find that the behavioral variability is altered
by learning, such that worms are less variable after training compared to naive
ones. The model further predicts the learning-dependent response and
variability under optogenetic perturbation of the olfactory neuron
AWC. Lastly, we investigate neural circuits downstream from
AWC that are differentially recruited for learned odor-guided
navigation. Together, we provide a new paradigm to quantify flexible navigation
algorithms and pinpoint the underlying neural substrates
Inhibitory feedback from the motor circuit gates mechanosensory processing in C. elegans
Animals must integrate sensory cues with their current behavioral context to
generate a suitable response. How this integration occurs is poorly understood.
Previously we developed high throughput methods to probe neural activity in
populations of Caenorhabditis elegans and discovered that the animal's
mechanosensory processing is rapidly modulated by the animal's locomotion.
Specifically we found that when the worm turns it suppresses its
mechanosensory-evoked reversal response. Here we report that C. elegans use
inhibitory feedback from turning-associated neurons to provide this rapid
modulation of mechanosensory processing. By performing high-throughput
optogenetic perturbations triggered on behavior, we show that turning
associated neurons SAA, RIV and/or SMB suppress mechanosensory-evoked reversals
during turns. We find that activation of the gentle-touch mechanosensory
neurons or of any of the interneurons AIZ, RIM, AIB and AVE during a turn is
less likely to evoke a reversal than activation during forward movement.
Inhibiting neurons SAA, RIV and SMB during a turn restores the likelihood with
which mechanosensory activation evokes reversals. Separately, activation of
premotor interneuron AVA evokes reversals regardless of whether the animal is
turning or moving forward. We therefore propose that inhibitory signals from
SAA, RIV and/or SMB gate mechanosensory signals upstream of neuron AVA. We
conclude that C. elegans rely on inhibitory feedback from the motor circuit to
modulate its response to sensory stimuli on fast timescales. This need for
motor signals in sensory processing may explain the ubiquity in many organisms
of motor-related neural activity patterns seen across the brain, including in
sensory processing areas
Simultaneous optogenetic manipulation and calcium imaging in freely moving C. elegans
A fundamental goal of systems neuroscience is to probe the dynamics of neural
activity that drive behavior. Here we present an instrument to simultaneously
manipulate neural activity via Channelrhodopsin, monitor neural response via
GCaMP3, and observe behavior in freely moving C. elegans. We use the instrument
to directly observe the relation between sensory stimuli, interneuron activity
and locomotion in the mechanosensory circuit
Correcting motion induced fluorescence artifacts in two-channel neural imaging
Imaging neural activity in a behaving animal presents unique challenges in
part because motion from an animal's movement creates artifacts in fluorescence
intensity time-series that are difficult to distinguish from neural signals of
interest. One approach to mitigating these artifacts is to image two channels;
one that captures an activity-dependent fluorophore, such as GCaMP, and another
that captures an activity-independent fluorophore such as RFP. Because the
activity-independent channel contains the same motion artifacts as the
activity-dependent channel, but no neural signals, the two together can be used
to remove the artifacts. Existing approaches for this correction, such as
taking the ratio of the two channels, do not account for channel independent
noise in the measured fluorescence. Moreover, no systematic comparison has been
made of existing approaches that use two-channel signals. Here, we present
Two-channel Motion Artifact Correction (TMAC), a method which seeks to remove
artifacts by specifying a generative model of the fluorescence of the two
channels as a function of motion artifact, neural activity, and noise. We
further present a novel method for evaluating ground-truth performance of
motion correction algorithms by comparing the decodability of behavior from two
types of neural recordings; a recording that had both an activity-dependent
fluorophore (GCaMP and RFP) and a recording where both fluorophores were
activity-independent (GFP and RFP). A successful motion-correction method
should decode behavior from the first type of recording, but not the second. We
use this metric to systematically compare five methods for removing motion
artifacts from fluorescent time traces. We decode locomotion from a GCaMP
expressing animal 15x more accurately on average than from control when using
TMAC inferred activity and outperform all other methods of motion correction
tested.Comment: 11 pages, 3 figure
Recommended from our members
Optogenetic Manipulation Of Neural Activity In Freely Moving Caenorhabditis elegans
We present an optogenetic illumination system that is capable of real-time light delivery with high spatial resolution to specified cellular targets in freely moving C. elegans. In our system, a tracking microscope and high-speed video camera records the posture and motion of an unrestrained worm expressing Channelrhodopsin-2 or Halorhodopsin/NpHR in specific cell types. Custom image processing software analyzes the position of a worm within each video frame, and then rapidly estimates the locations of targeted cells. The software then instructs a digital micromirror device to illuminate targeted cells with laser light of the appropriate wavelengths to stimulate or inhibit activity. Since each cell in an unrestrained worm is a rapidly moving target, our imaging and analysis system operates at high speed frames per second) to provide high spatial resolution . To demonstrate the accuracy, flexibility, and utility of our system, we present optogenetic analyses of the worm motor circuit, egg-laying circuit, and mechanosensory circuits that were not possible with previous methods.Physic
Prospective Evaluation of the Influence of Iterative Reconstruction on the Reproducibility of Coronary Calcium Quantification in Reduced Radiation Dose 320 Detector Row CT.
BACKGROUND: Coronary artery calcium (CAC) predicts coronary heart disease events and is important for individualized cardiac risk assessment. This report assesses the interscan variability of CT for coronary calcium quantification using image acquisition with standard and reduced radiation dose protocols and whether the use of reduced radiation dose acquisition with iterative reconstruction (IR; reduced-dose/IR ) allows for similar image quality and reproducibility when compared to standard radiation dose acquisition with filtered back projection (FBP; standard-dose/FBP ) on 320-detector row computed tomography (320-CT).
METHODS: 200 consecutive patients (60 ± 9 years, 59% male) prospectively underwent two standard- and two reduced-dose acquisitions (800 total scans, 1600 reconstructions) using 320 slice CT and 120 kV tube voltage. Automated tube current modulation was used and for reduced-dose scans, prescribed tube current was lowered by 70%. Image noise and Agatston scores were determined and compared.
RESULTS: Regarding stratification by Agatston score categories (0, 1-10, 11-100, 101-400, \u3e400), reduced-dose/IR versus standard-dose/FBP had excellent agreement at 89% (95% CI: 86-92%) with kappa 0.86 (95% CI: 0.81-0.90). Standard-dose/FBP rescan agreement was 93% (95% CI: 89-96%) with kappa = 0.91 (95% CI: 0.86-0.95) while reduced-dose/IR rescan agreement was similar at 91% (95% CI: 87-94%) with kappa 0.88 (95% CI: 0.83-0.93). Image noise was significantly higher but clinically acceptable for reduced-dose/IR (18 Hounsfield Unit [HU] mean) compared to standard-dose/FBP (16 HU; p \u3c 0.0001). Median radiation exposure was 74% lower for reduced- (0.37 mSv) versus standard-dose (1.4 mSv) acquisitions.
CONCLUSION: Rescan agreement was excellent for reduced-dose image acquisition with iterative reconstruction and standard-dose acquisition with filtered back projection for the quantification of coronary calcium by CT. These methods make it possible to reduce radiation exposure by 74%.
CLINICAL TRIAL REGISTRATION: URL: https://clinicaltrials.gov/ct2/show/NCT01621594.
UNIQUE IDENTIFIER: NCT01621594
- …