image: Winner of the Paul Ehrlich and Ludwig Darmstaedter Early Career Award 2025: Tobias Ackels from University of Bonn.
Credit: Rolf Mueller, University of Bonn
FRANKFURT. Many animal species would not be able to survive without their sense of smell. They rely on it to locate food sources, find mates and avoid predators. For nocturnal animals, it is the most important tool for sniffing their way around dark spaces. That being said, “smelling” is no easy feat, given that every smell is made up of many different molecules and every natural scent cloud in turn consists of many different odors. Until now, a sniff was considered the smallest unit of information in odor processing – an assumption Tobias Ackels has proven to be false. To do so, he constructed an odor application device that allows him to release individual or mixed odors through valves in precise millisecond pulses. The experiment showed that even between each individual sniff, mammals absorb information that can control their behavior.
In mice, as in humans, odors are registered by olfactory cells in the nasal mucosa. Each of these nerve cells carries only one type of olfactory receptor. Mice have more than 1,000 such types, humans around 350, with a few thousand olfactory cells each carrying the same receptor. Once an odorant binds to this receptor, it triggers a – relatively slow – signaling cascade inside the cell: It transmits an information wave via the main cable (axon) of the relevant olfactory cell, which in turn leads to a kind of circuit station in the olfactory bulb at the base of the brain. Information from the axons of a single receptor type’s olfactory cells converges inside each such switching station (glomerulus) – with a slight time delay, because these cells are widely distributed in the nasal mucosa and therefore not all reached by “their smell” at the same time. This delayed convergence increases the information content delivered by the signals from the olfactory cells, which are mapped as a scent reservoir in the nervous input of the olfactory bulb, stored in the nasal mucosa after each breath, thereby making it receptive to rapidly changing stimuli that would otherwise be lost. Tobias Ackels first confirmed this hypothesis in a computer model and then in fluorescence microscopy measurements of nerve cell activity in mice exposed to such stimuli.
Simulating the situation in a natural environment, Ackels then presented synchronously or asynchronously correlated mixtures of two scents to a group of thirsty mice, whereby synchronous odors come from the same, and asynchronous odors from different places. Half of the mice were rewarded with water when they recognized a synchronous stimulus, the other half when they recognized an asynchronous stimulus. Both groups learned the difference and mastered it up to a frequency of 40 Hertz – suggesting that, to orient themselves in space, mammals can use this ability to differentiate between the sources of different odor signals at lightning speed. This ability is also important for us humans: we can smell a forest fire, for example, before we see it.
Ackels showed that this ability is encoded in the output of the olfactory bulb, i.e. in the mitral and tufted cells that, without taking a detour via the diencephalon, send the odor information from the glomeruli directly to the cortex of the olfactory brain and the limbic system, both of which are particularly strongly linked to emotion and memory. The only mediators integrated into these circuits are interneurons, granule cells in particular, which renew themselves in the olfactory bulb throughout life – disproving the former dogma that adult nerve cells are no longer capable of dividing. With the support of the European Research Council (ERC), Tobias Ackels is currently investigating how these cells contribute to extracting information from the olfactory bulb and communicating it to higher brain regions. Given that interneurons are increasingly regarded as the conductors of feeling and thinking, his findings could be of exemplary importance. There are also increasing signs that olfactory deficits precede the structural changes, memory impairment and clinical symptoms associated with dementia and could therefore be used for early detection – which could open the door for a translation of his basic research, a prospect about which Tobias Ackels is in close contact with clinicians at the Deutsches Zentrum für neurodegenerative Erkrankungen (DZNE, German Center for Neurodegenerative Diseases) in Bonn.
Prof. Dr. rer. nat. Tobias Ackels studied biology at RWTH Aachen University from 2005 to 2011. He received his doctorate there in 2015 with a thesis on signal processing in the olfactory system of mammals. From 2015 to 2023, he was a postdoctoral researcher in Prof. Andreas Schäfer’s group at the Francis Crick Institute in London. In August 2023, he returned to Germany and took up a W2 professorship at the University of Bonn, where he heads the Sensory Dynamics and Behavior group at the Institute of Experimental Epileptology and Cognition Research at the University Hospital Bonn. In the same year, he was awarded an ERC Starting Grant.
The prize will be awarded – together with the main prize 2025 –by the Chairman of Paul Ehrlich Foundation’s Scientific Council in Frankfurt's Paulskirche on March 14, 2025 at 5 p.m.
Pictures of the award winner and detailed background information “On the trail of the deepest sense” are available for download at: www.paul-ehrlich-stiftung.de