Self-motion leads to mandatory cue fusion across sensory modalities

When perceiving properties of the world, we effortlessly combine multiple sensory cues into optimal estimates. Estimates derived from the individual cues are generally retained once the multisensory estimate is produced and discarded only if the cues stem from the same sensory modality (i.e., mandatory fusion). Does multisensory integration differ in that respect when the object of perception is one's own body, rather than an external variable? We quantified how humans combine visual and vestibular information for perceiving own-body rotations and specifically tested whether such idiothetic cues are subjected to mandatory fusion. Participants made extensive size comparisons between successive whole body rotations using only visual, only vestibular, and both senses together. Probabilistic descriptions of the subjects' perceptual estimates were compared with a Bayes-optimal integration model. Similarity between model predictions and experimental data echoed a statistically optimal mechanism of multisensory integration. Most importantly, size discrimination data for rotations composed of both stimuli was best accounted for by a model in which only the bimodal estimator is accessible for perceptual judgments as opposed to an independent or additive use of all three estimators (visual, vestibular, and bimodal). Indeed, subjects' thresholds for detecting two multisensory rotations as different from one another were, in pertinent cases, larger than those measured using either single-cue estimate alone. Rotations different in terms of the individual visual and vestibular inputs but quasi-identical in terms of the integrated bimodal estimate became perceptual metamers. This reveals an exceptional case of mandatory fusion of cues stemming from two different sensory modalities

Orientation preference maps in Microcebus murinus reveal size-invariant design principles in primate visual cortex

Orientation preference maps (OPMs) are a prominent feature of primary visual cortex (V1) organization in many primates and carnivores. In rodents, neurons are not organized in OPMs but are instead interspersed in a ‘‘salt and pepper’’ fashion, although clusters of orientation-selective neurons have been reported. Does this fundamental difference reflect the existence of a lower size limit for orientation columns (OCs) below which they cannot be scaled down with decreasing V1 size? To address this question, we examined V1 of one of the smallest living primates, the 60-g prosimian mouse lemur (Microcebus murinus). Using chronic intrinsic signal imaging, we found that mouse lemur V1 contains robust OCs, which are arranged in a pinwheel-like fashion. OC size in mouse lemurs was found to be only marginally smaller compared to the macaque, suggesting that these circuit elements are nearly incompressible. The spatial arrangement of pinwheels is well described by a common mathematical design of primate V1 circuit organization. In order to accommodate OPMs, we found that the mouse lemur V1 covers one-fifth of the cortical surface, which is one of the largest V1-to-cortex ratios found in primates. These results indicate that the primate-type visual cortical circuit organization is constrained by a size limitation and raises the possibility that its emergence might have evolved by disruptive innovation rather than gradual change

Duration of Purkinje cell complex spikes increases with their firing frequency

Climbing fiber (CF) triggered complex spikes (CS) are massive depolarization bursts in the cerebellar Purkinje cell (PC), showing several high frequency spikelet components (\ub1600 Hz). Since its early observations, the CS is known to vary in shape. In this study we describe CS waveforms, extracellularly recorded in awake primates (Macaca mulatta) performing saccades. Every PC analyzed showed a range of CS shapes with profoundly different duration and number of spikelets. The initial part of the CS was rather constant but the later part differed greatly, with a pronounced jitter of the last spikelets causing a large variation in total CS duration. Waveforms did not effect the following pause duration in the simple spike (SS) train, nor were SS firing rates predictive of the waveform shapes or vice versa. The waveforms did not differ between experimental conditions nor was there a preferred sequential order of CS shapes throughout the recordings. Instead, part of their variability, the timing jitter of the CS\u2019s last spikelets, strongly correlated with interval length to the preceding CS: shorter CS intervals resulted in later appearance of the last spikelets in the CS burst, and vice versa. A similar phenomenon was observed in rat PCs recorded in vitro upon repeated extracellular stimulation of CFs at different frequencies in slice experiments. All together these results strongly suggest that the variability in the timing of the last spikelet is due to CS frequency dependent changes in PC excitability

LSST Science Book, Version 2.0

A survey that can cover the sky in optical bands over wide fields to faint magnitudes with a fast cadence will enable many of the exciting science opportunities of the next decade. The Large Synoptic Survey Telescope (LSST) will have an effective aperture of 6.7 meters and an imaging camera with field of view of 9.6 deg^2, and will be devoted to a ten-year imaging survey over 20,000 deg^2 south of +15 deg. Each pointing will be imaged 2000 times with fifteen second exposures in six broad bands from 0.35 to 1.1 microns, to a total point-source depth of r~27.5. The LSST Science Book describes the basic parameters of the LSST hardware, software, and observing plans. The book discusses educational and outreach opportunities, then goes on to describe a broad range of science that LSST will revolutionize: mapping the inner and outer Solar System, stellar populations in the Milky Way and nearby galaxies, the structure of the Milky Way disk and halo and other objects in the Local Volume, transient and variable objects both at low and high redshift, and the properties of normal and active galaxies at low and high redshift. It then turns to far-field cosmological topics, exploring properties of supernovae to z~1, strong and weak lensing, the large-scale distribution of galaxies and baryon oscillations, and how these different probes may be combined to constrain cosmological models and the physics of dark energy.Comment: 596 pages. Also available at full resolution at http://www.lsst.org/lsst/sciboo

Adaptive Kontrolle der Okkulomotorik durch das Kleinhirn: Lokalisation der Plastizität und der Funktionsmechanismen

The seeming ease with which our central nervous system adapts to continual physiological changes or learns new motor skills is quite impressive. Due to the wealth of knowledge about its neuronal underpinnings the preferred model for investigating such adaptive processes has been the oculomotor system. Surgical lesions in animals and studies of patients with cerebellar pathologies reveal that the absence of a normal functioning cerebellum impairs the ability to adapt motor behavior to any novel changes in the physical dynamics of the muscular periphery or in the external environment. The work presented in this thesis uses the oculomotor system as a model of biological motor control to investigate important aspects of cerebellum-dependent motor adaptation. It provides novel evidence that the cerebellum does not only act to compensate for external or physical changes but also for central disturbances within the brain itself that compromise accurate motor performance. It identifies at which stage of neural processing within the microcircuitry of the cerebellum the behaviorally relevant plasticity first occurs and what extra-cerebellar structures it influences to induce the learned motor response.Die scheinbare Leichtigkeit, mit der sich unser zentrales Nervensystem and sich kontinuierlich verändernde physiologischen Bedingungen anpasst, und mit der neue motorische Fertigkeiten erlernt werden, ist beeindruckend. Das okulomotorische System war aufgrund der Wissensfülle über seine neuronalen Grundlagen seit jeher das bevorzugte Modell für die Untersuchung solcher adaptiver Prozesse. Chirurgische Läsionen bei Tieren und Studien an Patienten mit zerebellären Erkrankungen zeigen, dass das Fehlen eines intakten Kleinhirns die Fähigkeit das motorische Verhalten an sich verändernde Umgebungsbedingen, stark beeinträchtigt. Die vorliegende Arbeit bedient sich des okulomotorischen Systems als ein Modell für biologische motorische Steuerung um wichtige Aspekte der Kleinhirn-abhängige Adaptation desselben zu untersuchen. Die Arbeit liefert neue Beweise dafür, dass das Kleinhirn nicht nur auf äussere Einflüsse hin reagiert, sondern sein Verhalten auch aufgrund zentraler Hirnprozesse anpasst um eine akkurate motorische Leistung aufrecht zu erhalten. Die Arbeit untersucht weiterhin, zu welchem Zeitpunkt innerhalb der neuronalen Verarbeitung des Kleinhirns die verhaltensrelevante Plastizität zuerst eintritt und welche extra-zerebellären Strukturen dadurch beeinflusst werden um eine bereits erlernte motorische Antwort herbeizuführen

Fusing slow and fast phases in a model of combined eye and head movements

A switching strategy mediated by brainstem omni-directional pause neurons (OPNs) is proposed to fuse slow and fast phases of orienting eye and head movements in a model of gaze control. It is implemented in the anatomically based model developed by Galiana and Guitton (1992) where slow and fast components of gaze are represented as two different operating modalities of the same neural circuit. No comprehensive mechanism for alternating between the two modes of operation yet exists; it is in fact one of the least understood aspects of oculomotor control. Switching strategies that are implemented in existing models are usually designed artificially just to obtain a desired system response. The mechanism presented in this thesis employs a linear weighted sum of three anatomically relevant inputs to OPNs; gaze motor error, head velocity and eye velocity. It is designed to accurately decide when one phase should be ended and the other initiated in all types of behaviorally observed gaze movements. Simulated performance reveals that the implemented switching mechanism compels the model to respond appropriately to both visual and vestibular stimuli

Inference of perceptual priors from path dynamics of passive self-motion

The monitoring of one's own spatial orientation depends on the ability to estimate successive self-motion cues accurately. This process has become to be known as path integration. A feature of sequential cue estimation, in general, is that the history of previously experienced stimuli, or priors, biases perception. Here, we investigate how during angular path integration, the prior imparted by the displacement path dynamics affects the translation of vestibular sensations into perceptual estimates. Subjects received successive whole-body yaw rotations and were instructed to report their position within a virtual scene after each rotation. The overall movement trajectory either followed a parabolic path or was devoid of explicit dynamics. In the latter case, estimates were biased toward the average stimulus prior and were well captured by an optimal Bayesian estimator model fit to the data. However, the use of parabolic paths reduced perceptual uncertainty, and a decrease of the average size of bias and thus the weight of the average stimulus prior were observed over time. The produced estimates were, in fact, better accounted for by a model where a prediction of rotation magnitude is inferred from the underlying path dynamics on each trial. Therefore, when passively displaced, we seem to be able to build, over time, from sequential vestibular measurements an internal model of the vehicle's movement dynamics. Our findings suggest that in ecological conditions, vestibular afference can be internally predicted, even when self-motion is not actively generated by the observer, thereby augmenting both the accuracy and precision of displacement perception

Rapid Integration of Artificial Sensory Feedback during Operant Conditioning of Motor Cortex Neurons

Neuronal motor commands, whether generating real or neuroprosthetic movements, are shaped by ongoing sensory feedback from the displacement being produced. Here we asked if cortical stimulation could provide artificial feedback during operant conditioning of cortical neurons. Simultaneous two-photon imaging and real-time optogenetic stimulation were used to train mice to activate a single neuron in motor cortex (M1), while continuous feedback of its activity level was provided by proportionally stimulating somatosensory cortex. This artificial signal was necessary to rapidly learn to increase the conditioned activity, detect correct performance, and maintain the learned behavior. Population imaging in M1 revealed that learning-related activity changes are observed in the conditioned cell only, which highlights the functional potential of individual neurons in the neocortex. Our findings demonstrate the capacity of animals to use an artificially induced cortical channel in a behaviorally relevant way and reveal the remarkable speed and specificity at which this can occur