Past events

Spatial learning is a complex behavior which includes, among others, encoding of space, sensory and motivational processes, arousal and locomotor performance. Today, our view on spatial navigation is largely hippocampus-centrist. Less is known about the involvement of brain structures up- and downstream, or out of this circuit. Here, we provide the fist in vivo assessment of the neural matrix underlying spatial learning, using functional manganese-enhanced MRI (MEMRI) and voxel-wise whole brain analysis. Mice underwent place-learning (PL) vs. response-learning (RL) in the water cross maze (WCM) and its readout was correlated to the Mn2+ contrasts. Thus, we identified structures involved in spatial learning largely overlooked in the past, due to methods focused on region of interest (ROI) analyses. Add-on experiments pointed to bias in Mn2+ accumulati! on towards projection terminals, suggesting that our mapping was mostly formed by projection sites of the originally activated structures. This is corroborated by in-depth analysis of MEMRI data after WCM learning showing mostly downstream targets of the hippocampus. These differ between fornical afferences from vCA1 and direct innervation from dCA1/iCA1 (for PL), and structures along the longitudinal association bundle originating in vCA1 (for RL). To elucidate the pattern of Mn2+ accumulation seen on the scans we performed c-fos expression analyses following learning in the WCM. This helped us identify the structures initially activated during spatial learning and its underlying connectivity to establish the matrix. Finally, to test the causal involvement of these structures we inhibited them (through DREADDs) while mice performed in the WCM task. We also focused on the causal involvement of the mPFC-HPC circuit on strategy switch during WCM learning. We believe that this study might shed light into new brain structures involved in spatial learning and strategy switch and complement the current knowledge on these circuits’ connectivity. Moreover, we elucidated some functional mechanisms of MEMRI, clarifying the interpretation of data obtained with this method and its possible future applications.

Understanding how social influence shapes biological processes is a central challenge in contemporary science, essential for achieving progress in a variety of fields ranging from the organization and evolution of coordinated collective action among cells, or animals, to the dynamics of information exchange in human societies. Using an integrated experimental and theoretical approach I will address how, and why, animals exhibit highly-coordinated collective behavior. I will demonstrate new imaging and virtual reality (VR) technology that allows us to reconstruct (automatically) the dynamic, time-varying sensory networks by which social influence propagates in groups. This allows us to identify, for any instant in time, the most socially-influential individuals, to reveal the (counterintuitive) relationship between network structure and social contagion, and to predict the magnitude of complex behavioural cascades within groups before they actually occur. By investigating the coupling between spatial and information dynamics in groups we also demonstrate that emergent problem solving is the predominant mechanism by which mobile groups sense, and respond to complex environmental gradients. Finally I will reveal the critical role uninformed, or unbiased, individuals play in effecting fast, democratic consensus decision-making in collectives, and will test these predictions with experiments involving schooling fish and wild baboons, as well as suggest how such results may relate to decision-making in neural systems.

The introduction of two-photon microscopy for in vivo imaging has opened the door to chronic monitoring of individual neurons in the adult brain and the study of structural plasticity mechanisms at a very fine scale. Perhaps the biggest contribution of this modern anatomical method has been the discovery that even across the stable excitatory dendritic scaffold there is significant capacity for synaptic remodeling, and that synaptic structural rearrangements are a key mechanism mediating neural circuit adaptation and behavioral plasticity in the adult. To monitor the extent and nature of excitatory and inhibitory synapse dynamics on individual L2/3 pyramidal neurons in mouse visual cortex in vivo, we labeled these neurons with a fluorescent cell fill as well as the fluorescently tagged synaptic scaffolding molecules, Teal-Gephyrin to label inhibitory synapses, and mCherry-PSD-95 to label excitatory synapses. We simultaneously tracked the daily dynamics of both synapse types using spectrally resolved two-photon microscopy. We found that aside from the lower magnitude of excitatory synaptic changes in the adult, as compared to inhibitory ones, excitatory synapse dynamics appear to follow a different logic than inhibitory dynamics. While excitatory dynamics seem to follow a sampling strategy to search for and create connections with new presynaptic partners, inhibitory synapse dynamics likely serve to locally modulate gain at specific cellular locales.