Past events

Although animals and humans move daily through complex three-dimensional (3D) environments, practically nothing is known about the encoding of 3D head direction in the brain. Moreover, very little is known about how neural circuits represent the location or direction of spatial goals – which is essential for goal-directed navigation. In the first part of the talk, I will present the first neural recordings of 3D head-direction cells from the hippocampal formation of flying and crawling bats, and will describe the functional organization and the surprising properties of these neurons. By using the head-direction system as an example, I will also discuss several theoretical considerations for the existence of both pure and conjunctive population codes in the brain. In the second part, I will present our new findings that suggest the existence of goal-direction and goal-proximity signals in the bat hippocampus – a vectorial representation that could support goal-directed navigation.

From detecting food to locating lurking predators, visual search -- the ability to find an object of interest against a background -- needs to be accurate and fast to ensure survival. In mammals, this led to the development of a parallel search mode, pop-out, which enables fast detection time that is not dependent on the number of distracting objects. Although it may be beneficial to most animals, pop-out behavior has been observed only in mammals, where its neural correlates are found as early as V1 in contextually modulated cells that encode aspects of saliency. I will describe our recent findings of pop-out visual search in the archer fish and discuss possible implications about universality of visual search among vertebrates.

Bats have a unique view of the world: ‘seeing’ their environment with their ears through echolocation. They use this active sensing system to master their predominantly dark world, e.g. for detecting and targeting of small insect prey, navigating through complex vegetation or interaction with other individuals. Over the last decades we have developed a solid understanding of how bats apply echolocation to achieve this. However, many questions are still unsolved, e.g. assessment of larger objects like trees or even whole habitats. In my talk, I will show how bats recognize and deal with water surfaces. My results demonstrate that a recognition pattern can be very simple: for bats any smooth surface is perceived as a water surface. Likely through a long evolutionary consolidation without any contradicting experiences, this is phylogenetically wide spread among bats, extremely hardwired and even innate. In addition I will talk about the integration of varying sensory input, the role of spatial memory and potential evolutionarytraps that may arise from this. Echolocation is a rather short-ranged sensing system, which leaves the intriguing question of how bats orientate and navigate over long distances. They face this challenge not only during daily foraging trips but also on migration routes which can be over 1,000 kilometers long. Recent evidence has shown that bats can, for example, make use of the Earth’s magnetic field. However, the exact functional mechanism of this ability is as yet largely unknown. In this context, I will present data showing that our tested bat species recognizes the sky’s polarization pattern at dusk and uses it as a calibrating system for its magnetic compass. This is the only known case so far for a mammal to use this sensory light cue.

Although animals and humans move daily through complex three-dimensional (3D) environments, practically nothing is known about the encoding of 3D head direction in the brain. Moreover, very little is known about how neural circuits represent the location or direction of spatial goals – which is essential for goal-directed navigation. In the first part of the talk, I will present the first neural recordings of 3D head-direction cells from the hippocampal formation of flying and crawling bats, and will describe the functional organization and the surprising properties of these neurons. By using the head-direction system as an example, I will also discuss several theoretical considerations for the existence of both pure and conjunctive population codes in the brain. In the second part, I will present our new findings that suggest the existence of goal-direction and goal-proximity signals in the bat hippocampus – a vectorial representation that could support goal-directed navigation.

One fundamental question in neuroscience remains largely unanswered: how are computations implemented by structured neural circuits? Over the last fifty years we have learned how sensory, motor and cognitive information is represented in different regions of the mammalian brain. Anatomical studies are beginning to reveal precisely structured neural circuits, including stereotyped circuit motifs across brain areas subserving different functions. However, linking physiology and detailed anatomy remains elusive in most cases. We know little about activity in specific cell types, the nodes of the circuit diagram, in behaving animals. In our lab we study how tactile information is represented in different brain circuits in the mice vibrissal system. We train mice to move their whiskers to judge the location of an object presented in one of several locations and record extra- and intracellularly from specific neural types in this circuit. I’ll present recent results showing how tactile information is processed and transformed by specific neural types and circuits as it ascends from the sensory periphery to cortex.

Many experiments provide evidences that, after learning, human and animal memories are very dynamic and changeable. Amongst others, one intriguing and counterintuitive effect is the destabilization of memories by recalling them. In addition, some of these destabilized memories can be ‘rescued’ by sleep-induced consolidation while others not. Up to now, the basic principles underlying these effects are widely unknown. In this talk I will present our theoretical model in which the interaction between the biologically well-established processes of synaptic plasticity and scaling enables the formation of memories or rather Hebbian cell assemblies in neural networks. Furthermore, we can show that the dynamics of these cell assemblies are comparable to the intriguing dynamics of human and animal memories described above. Thus, this model serves as a further step to link biological processes on the neuronal scale to behavior on the psychological level.