Rumpel Group Research
Auditory perception and memory in the neocortex
Our lab is focused on the development, function, and plasticity of neuronal circuits. Specifically, we would like to know how memory is stored over long periods of time. This is fundamental in understanding the mind: memories of past experiences shape our personalities and influence our current perception.
A look at the brain
- Figure 1 (Click to view legend)
Long-term storage of information about relevant experiences is essential for successful adaptation of human and animal behavior in a changing environment. A current model of memory formation suggests plastic adaptations in neuronal connections (synapses) caused by relevant experiences. Yet, how such changes in synaptic connectivity lead to the formation of a memory trace remains elusive. How is the processing of external stimuli altered after the formation of a memory? How are we able to continuously store novel memories in a given neuronal circuit without corrupting previously stored memories? In order to understand the mechanisms by which multiple memory traces are coordinated, we are currently applying in vivo imaging techniques to the auditory cortex of mice. The auditory cortex mediates processing of sounds and is involved in the formation of memories of sounds.
- Figure 2 (Click to view legend)
Two-photon laser scanning microscopy in transgenic animals expressing green fluorescent protein in just a small subset of cells permits the same neurons, and even the same individual synapses, to be revisited day after day. This is truly remarkable because we estimate that the brain comprises about 10 trillion (1013) synapses. We find that neocortical circuits are highly dynamic: remodeling occurs by the formation/elimination of synaptic connections as well as adaptations in the strength of existing connections. We are currently investigating the impact of auditory learning paradigms on the dynamics of a given set of synapses in the auditory cortex.
- Figure 3 (Click to view legend)
In vivo imaging not only permits analysis of synaptic connections, but also monitoring of neuronal activity in tens of neurons simultaneously. Action potential-mediated increases in calcium levels can be detected as changes in fluorescence of calcium indicators. We are investigating activity patterns elicited by various sounds in neuronal populations of the auditory cortex in order to learn about the principles how sounds are encoded and recognized in the brain. We observe that activity in layer 2/3 neuronal ensembles is surprisingly strongly constrained into very few response modes. Interestingly, these discrete activity modes can serve as a representational basis to predict generalization behavior in an auditory discrimination task. Our findings point toward a model of neocortical function in which external stimuli are represented in a broad basis set of spontaneous associations into common activity patterns, and classified by sharp transition across the activity patterns. In the future we will investigate the circuit mechanisms that lead to the generation of sounds representations in discrete activity modes, and to what extent auditory learning paradigms cause changes in these neuronal representations of memorized sounds.
Jointly, these approaches will pave the way for a series of novel experiments addressing the storage of information in living neuronal networks: a field of research that has been almost exclusively the domain of theoretical neuroscientists thus far.