Self-perception: mechanosensation and beyond
Brain-organ communications play a crucial role in maintaining the body's physiological and psychological homeostasis, and are controlled by complex neural and hormonal systems, including the internal mechanosensory organs. However, the progress has been slow due to technical hurdles: the sensory neurons are deeply buried inside the body and are not readily accessible for direct observation, the projection patterns from different organs or body parts are complex rather than converging into dedicate brain regions, the coding principle cannot be directly adapted from that learned from conventional sensory pathways. Our lab apply the pipeline of "biophysics of receptors-cell biology of neurons-functionality of neural circuits-animal behaviors" to explore the molecular and neural mechanisms of self-perception. In the lab, we mainly focus on the following three questions: 1, The molecular and cellular basis for proprioception and interoception. 2, The circuit mechanisms of sensory coding and integration of internal and external information. 3, The function of interoception in regulating behavior homeostasis.
A Panoramic View on Vision
Statistics of natural scenes are not uniform - their structure varies dramatically from ground to sky. It remains unknown whether these non-uniformities are reflected in the large-scale organization of the early visual system and what benefits such adaptations would confer. By deploying an efficient coding argument, we predict that changes in the structure of receptive fields across visual space increase the efficiency of sensory coding. To test this experimentally, developed a simple, novel imaging system that is indispensable for studies at this scale. In agreement with our predictions, we could show that receptive fields of retinal ganglion cells change their shape along the dorsoventral axis, with a marked surround asymmetry at the visual horizon. Our work demonstrates that, according to principles of efficient coding, the panoramic structure of natural scenes is exploited by the retina across space and cell-types.
Sensory and metasensory responses during sequence learning in the mouse somatosensory cortex
Sequential temporal ordering and patterning are key features of natural signals, used by the brain to decode stimuli and perceive them as sensory objects. Touch is one sensory modality where temporal patterning carries key information, and the rodent whisker system is a prominent model for understanding neuronal coding and plasticity underlying touch sensation. Neurons in this system are precise encoders of fluctuations in whisker dynamics down to a timescale of milliseconds, but it is not clear whether they can refine their encoding abilities as a result of learning patterned stimuli. For example, can they enhance temporal integration to become better at distinguishing sequences? To explore how cortical coding plasticity underpins sequence discrimination, we developed a task in which mice distinguished between tactile ‘word’ sequences constructed from distinct vibrations delivered to the whiskers, assembled in different orders. Animals licked to report the presence of the target sequence. Optogenetic inactivation showed that the somatosensory cortex was necessary for sequence discrimination. Two-photon imaging in layer 2/3 of the primary somatosensory “barrel” cortex (S1bf) revealed that, in well-trained animals, neurons had heterogeneous selectivity to multiple task variables including not just sensory input but also the animal’s action decision and the trial outcome (presence or absence of the predicted reward). Many neurons were activated preceding goal-directed licking, thus reflecting the animal’s learnt action in response to the target sequence; these neurons were found as soon as mice learned to associate the rewarded sequence with licking. In contrast, learning evoked smaller changes in sensory response tuning: neurons responding to stimulus features were already found in naïve mice, and training did not generate neurons with enhanced temporal integration or categorical responses. Therefore, in S1bf sequence learning results in neurons whose activity reflects the learnt association between target sequence and licking, rather than a refined representation of sensory features. Taken together with results from other laboratories, our findings suggest that neurons in sensory cortex are involved in task-specific processing and that an animal does not sense the world independently of what it needs to feel in order to guide behaviour.
Microneurography And Microstimulation Of Single Tactile Afferents In The Human Hand
Microneurography is a method, invented by Ake Vallbo and Karl-Erik Hagbarth in the late 1960, with which we can record the activity from single, identified nerve fibres in awake human participants. In this talk, I will then discuss the method, its advantages and limitations, and some of the key discoveries regarding coding of tactile events in the signalling from receptors in the human skin. An extension of the method is to stimulate single afferents, and record the resulting tactile sensations reported by the participants, so-called microstimulation. The first experiments were done in the 1980s, but the method has recently seen a revival, and is currently being combined with high-resolution brain imaging in the study of the relationship between tactile nerve signals, sensations, and processing of tactile information in the brain.
A robust neural code for human odor in the Aedes aegpyti mosquito brain
A globally invasive form of the mosquito Aedes aegypti has evolved to specialize in biting humans, making it an efficient vector of dengue, yellow fever, Zika, and chikungunya. Host-seeking females identify humans primarily by smell, strongly preferring human odour over the odor of non-human animals. Exactly how they discriminate, however, is unclear. Human and animal odors are complex blends that share most of the same chemical components, presenting an interesting challenge in sensory coding. I will talk about recent work from the lab showing that (1) human and animal blends can be distinguished by the relative concentration of a diverse array of compounds and that (2) these complex chemical differences translate into a neural code for human odor that involves as few as two to three olfactory glomeruli in the mosquito brain. Our work demonstrates how organisms may evolve to discriminate complex odor stimuli of special biological relevance with a surprisingly simple combinatorial code and reveals novel targets for the design of next-generation mosquito control strategies.