スケジュール：

アブストラクト・関連論文：

伊藤　啓
Kei Ito
"Towards comprehensive "projectome" network analysis of the fly brain"

Revealing how all the neurons in the brain are interconnected should provide indispensable insights for understanding the brain function. Comprehensive knowledge about the projection patterns of all the neurons at cellular level, which can be called the projectome, is a prerequisite for such connectivity analyses. Taking advantage of the advanced molecular genetic tools and relatively simple brain structure, we are analyzing the neural networks of the fruit fly Drosophila. Specific groups of neurons are visualized using cell type- or lineage-specific gene expression induction system, and their functions are analyzed by expressing proteins that monitor or alter neural activities. Several examples of studies will be presented.

Kamikouchi, A., Inagaki, H. K., Effertz, T., Fiala, A., Hendrich, O., Gopfert, M. C. and Ito, K. The neural basis of Drosophila gravity sensing and hearing. Nature, 458, 165-171, 2009.

Tanaka, N. K., Tanimoto, H. and Ito, K. Neuronal assemblies of the Drosophila mushroom body. J Comp Neurol, 508, 711-755, 2008.

Miyazaki, T. and Ito, K. Neural architecture of the primary gustatory center of Drosophila melanogaster visualized with GAL4 and LexA enhancer-trap systems. J Comp Neurol, in press

Link





岡本　仁
Hitoshi Okamoto
"Habenula as the multimodal switching board for controlling bahaviors"

   The habenula is a part of an evolutionarily highly conserved  conduction pathway within the limbic system that connects  telencephalic nuclei to the interpeduncular nucleus (IPN) of the  midbrain. In mammals, the medial habenula receives inputs from the  septohippocampal system, and relaying such information to the IPN. In  contrast, the lateral habenula receives inputs from the ventral  pallidum, a part of the basal ganglia. The physical adjunction of  these two habenular nuclei suggests that the habenula may act as an intersection of the neural circuits for controlling emotion and  behavior. We have recently elucidated that zebrafish has the  equivalent structure as the mammalian habenula. Taking advantage of  the anatomical conservation of the habenula, we are now investigating  the physiological functions of the habenula by using both zebrafish  and rodents.
   The transgenic zebrafish, in which the neural signal transmission  from the lateral subnucleus of the dorsal habenula to the dorsal IPN  was selectively impaired, showed extremely enhanced levels of freezing  response to presentation of the conditioned aversive stimulus. This  result suggests this tract may normally function to suppress the  choice of freezing as a response to fear after establishment of fear conditioning. In rats, we discovered that the lateral habenula neurons  show during the REM sleep the phase-locked activity with the theta  oscillation detected in the hippocampus, which was severely reduced by 
ablation of the lateral habenula, implicating the lateral habenula as a modulatory gate for theta oscillation.
   These observations support that the habenula may act as the multimodal switching board for controlling emotional behaviors and/or memory in experience dependent manners.

Link





Marc Sommer

"Neuronal circuits for stable perception during eye movements"

A major challenge for the brain is to perceive the world accurately as we move through it. Each action we make disrupts sensory receptors by displacing them and distorting their inputs. Nevertheless, we are able to interact with the world and still perceive it clearly. A longstanding hypothesis has been that the brain accomplishes perception during action by monitoring internal warnings about movements known as corollary discharge. With corollary discharge information, a sensory area could predict the sensory consequences of movement and thus transform chaotic inputs into stable percepts. We have been studying the neuronal basis of corollary discharge in the visual and eye movement systems. Primates make saccadic eye movements around twice per second, displacing the retinal image each time, and yet they perceive the visual world as continuous and stable. We recorded from neurons in behaving monkeys and discovered that a corollary discharge of every saccade is sent from the superior colliculus (SC) via mediodorsal thalamus (MD) up to the frontal eye field (FEF). This signal influences a property of FEF visual neurons, known as presaccadic remapping, that may provide the neuronal basis of visual stability. Just before a saccade, FEF neurons remap their visual sensitivity to the location in absolute space where the receptive field will land after the saccade. In other words, the neurons "peek" at what they will see after the eyes move, allowing them to integrate the presaccadic and postsaccadic scenes. When we temporarily inactivated the SC-MD-FEF pathway, FEF neurons were severely impaired at presaccadic remapping. In sum, our results confirm the existence of a corollary discharge circuit in the primate brain and demonstrate that it affects sensory processing in a way that could lead to stable perception during action.

Related papers

Link to references

Two specific papers relevant to the talk would be:
Sommer, M.A. & Wurtz, R.H. (2002) A pathway in primate brain for internal monitoring of movements. Science 296: 1480-1482

Sommer, M.A. & Wurtz, R.H. (2006) Influence of the thalamus on spatial visual processing in frontal cortex. Nature 444: 374-377


Plus a review,
Sommer, M.A. & Wurtz, R.H. (2008) Brain circuits for the internal monitoring of movements. Annual Review of Neuroscience 31: 317-338






田中　真樹
Masaki Tanaka

"Cortico-subcortical mechanisms of temporal processing"

   Although both the cortico-basal ganglia and the cortico-cerebellar networks are implicated in temporal processing, how neurons in each network represent time remains largely unknown. We searched for the neuronal correlates of sensory and motor timing in trained monkeys and found different ways of time representation in the relevant networks.
   A widely accepted neural mechanism for keeping track of elapsed time is to monitor gradual increase of firing rate that approaches to a threshold. When we trained monkeys to make a self-initiated saccade 1.2 ± 0.4 s following a visual　cue, many neurons in the motor thalamus exhibited a strong buildup of activity. The time course of neuronal activity predicted the timing of self-initiated saccade, suggesting that the activity reflected monkey’s subjective experience of elapsed time in each trial. Because similar activity was also found in the globus pallidus and in the medial frontal cortex during the task, the basal ganglia-thalamocortical pathways might represent time by integrating neural signals over time.  We found a different way of time representation in the cerebellum. When monkeys were required to detect the absence or the changes in color of the repetitive visual stimuli that appeared periodically at a fixed interval, neurons in the deep cerebellar nuclei exhibited firing modulation that gradually increased as the repetition progressed. Importantly, the magnitude of firing modulation for each stimulus was positively correlated with the length of the inter-stimulus interval in a given trial. In other words, the sensory gain depended on the passage of time since the previous stimulus, suggesting that the cerebellum may represent time in a state-dependent manner. Because inactivation of the recording sites delayed the detection of the missing stimuli, and because a similar tendency was also found in cerebellar patients, the signals in the cerebellum are likely to be necessary to compute prediction error in the absence of expected stimulus. Thus, the basal ganglia and the cerebellum may contribute to different aspects of temporal processing that guide behavior.

References

Tanaka, M. (2006) Inactivation of the central thalamus delays self-timed saccades. Nature Neurosci. 9: 20-22.

Tanaka, M. (2007) Cognitive signals in the primate motor thalamus predict saccade timing. J. Neurosci. 27: 12109-12118.

Yoshida, A. & Tanaka, M. (2009) Enhanced modulation of neuronal activity during antisaccades in the primate globus pallidus. Cereb. Cortex 19: 206-217.

Kunimatsu,J. & Tanaka, M. (2010) Roles of the primate motor thalamus in the generation of antisaccades. J. Neurosci. 30: 5108-5117.

Link






Konrad Körding

"Causal inference in motor control and perception"

 Perceptual events derive their significance to an animal from their meaning about the world, that is from the information they carry about their causes. Here we use multisensory cue combination to study causal inference in perception and motor control. We formulate an ideal-observer model that infers whether two sensory cues have a common cause and that also estimates their location(s). This model accurately predicts the nonlinear integration of cues by human subjects in two auditory-visual localization tasks. We find strong evidence of the same rules for sensorimotor adaptation. The results show that indeed humans can efficiently infer the causal structure as well as the location of causes. By combining insights from the study of causal inference with the ideal-observer approach to sensory cue combination, we show that the capacity to infer causal structure is not limited to conscious, high-level cognition; it is also performed
continually and effortlessly in perception.

Related papers

Dokka K, Kenyon RV, Keshner EA, Kording KP (2010) Self versus Environment Motion in Postural Control. PLoS Comput Biol 6(2)



Wei K, Körding K (2009) Relevance of error: what drives motor adaptation? J Neurophysiol. 101(2)


Körding KP, Beierholm U, Ma WJ, Quartz S, Tenenbaum JB, et al. (2007) Causal Inference in Multisensory Perception. PLoS ONE 2(9)