10. Mai 2021, 16:00-18:00

A reservoir of decision strategies in the mouse frontal cortex

Dr. Zach Mainen

A decision is an exclusive commitment to one of several alternative actions. A decision strategy is an algorithm for how to decide: what things to pay attention to and how to process them. For example, some decision strategies are based on direct responses to observable stimuli ('model free') while others require inferences about hidden states ('model based'). Decision strategies, like attentional processes, should imply commitment of neural processing resources, but the nature and limits of those resources are not well understood. We've been exploring these issues by recording large neural ensembles in the frontal cortex of mice performing a foraging task that admits several possible strategies for deciding when to leave a foraging site. We formulate a model based on temporal integration and reset that unifies an ensemble of strategies (including both model-based and model-free) into a single algorithmic family. We find that at any given time, not just one but the entire family of strategies can be simultaneously decoded from these neural ensembles. Surprisingly, the ability to read out a particular strategy is independent of whether it is currently being deployed behaviorally. Such multiplexing of decision computations may allow for more flexible combination and switching of strategies. These findings suggest that actual decisions reveal only the tip of an iceberg of decision-relevant computations being executed within the brain. This work is led by Fanny Cazettes and in collaboration with Alfonso Renart.

 


31. Mai 2021, 16:00-18:00

The neurobiology of confidence: from statistics to neurons

Dr. Torben Ott

How confident are you? As humans, aware of our subjective sense of confidence, we can readily answer. Knowing your level of confidence helps to optimize both routine decisions such as whether to go back and check if the front door was locked and momentous ones like finding a partner for life. Yet the inherently subjective nature of confidence has limited investigations by neurobiologists. We have developed a conceptual framework that roots subjective confidence in a statistical computation that can be behaviorally studied in non-human animals, thus enabling to study its neural basis. In an economic decision task, we asked humans and rats to invest time into choices based on ambiguous sensory evidence. Both humans and rats invest time according to their degree of confidence, the probability that their choice was correct. Single neurons in rat orbitofrontal cortex encode statistical decision confidence and predict two confidence-guided behaviors: trial-by-trial time investment serving as confidence reports and learning of choices across trials, thereby revealing abstract representations of decision confidence in rat frontal cortex. This work paves the way for interrogating the neural circuits that mediate confidence-based economic decisions and sheds light on the neural basis of metacognitive abilities.

 


21. Juni 2021, 16:00-18:00

From vision to navigation and back

Prof. Dr. Matteo Carandini

Vision provides crucial guidance to navigation, and this guidance is a key function of the visual system. The communication between visual system and navigation system, however, appears to operate also in the opposite direction, with navigation strongly influencing vision. We recorded from populations of neurons in mice that navigate virtual environments and found modulation by spatial position in neurons throughout the visual cortex, including primary visual cortex (but not in its thalamic afferents). These navigational signals correlate with those in the hippocampus, and reflect the animal’s own estimate of position acquired through both vision and idiothetic cues. They are perhaps strongest in the parietal cortex, where cells respond to vision only during navigation. Position signals, therefore, appear remarkably early in the visual system and permeate its operation. Various properties of these signals, including modulation by hippocampal theta oscillations, suggest that they originate in the hippocampus or associated regions of the navigational system. This talk centers on work by Aman Saleem, Julien Fournier, and Mika Diamanti.

 


5. Juli 2021, 16:00-18:00

How failures in protein folding can lead to neurodegenerative diseases

Prof. Dr. Janine Kirstein

How can we use a nematode to understand the manifestation and progression of neurodegenerative diseases? On a cellular level, humans do not differ much from much simpler organisms. We use the nematode C. elegans to understand how mutations that lead to aberrant protein structures such as amyloid fibrils cause neurodegenerative diseases. The nematode can be easily genetically manipulated and we have expressed the Abeta peptide (Aβ1-42) in the neurons and used fluorescence lifetime imaging to visualize and also quantify the aggregation of Aβ1-42 as the animal ages. Notably, using our new AD model, we could map for the first time in any living animal the onset of Aβ aggregation. Aβ1-42  starts to form amyloid fibrils in a subset of cholinergic neurons of the anterior head ganglion, the six IL2 neurons. Targeted depletion of Aβ1-42 in these IL2 neurons led to a systemic delay of Aβ pathology and restored neuronal function. We are currently studying what renders specific neurons more susceptible for Aβ1-42 aggregation and assess the potential of molecular chaperones as therapeutic strategy to interfere with the pathological aggregation cascade of Aβ1-42.

 


12. Juli 2021, 16:00-18:00

What the mouse eye tells the brain and how the brain processes this visual message

Dr. Katrin Franke

To provide a compact and efficient input to the brain, sensory systems separate the incoming information into parallel feature channels. In the visual system, parallel processing starts in the retina. Here, the image is decomposed into multiple retinal ganglion cell (RGC) types, each selective for a specific set of visual features like motion, contrast or edges. Recent work in mice provides a thorough classification of RGCs, revealing that the retina sends approx. 40 distinct information channels to the brain. However, how (i) visual features arise within the retinal network, (ii) are integrated in downstream brain areas and (iii) relate to behavior remains poorly understood. In my talk, I will present recent work addressing these questions by focusing on color – a single visual feature and an important aspect of natural scenes. Specifically, we followed the neural representation of color across all retinal layers to primary visual cortex in mice and linked our findings to the statistics of mouse natural scenes and available behavioral data. With this, we hope to increase our understanding of how specific sensory features are processed across neural hierarchies to drive behavior – a central question in neuroscience.

 

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