Auditory Steady-State Response Deficits

Since synchronized neuronal activity is thought to underlie efficient communication in the brain and to be crucially involved in working memory processes, alterations of this synchrony, as found in electroencephalogram (EEG) or magnetoencephalogram (MEG) studies of patients suffering from schizophrenia (SCZ) might contribute to the symptoms in patients and impairments characterizing schizophrenia. One very robust finding in EEG/MEG studies of schizophrenia patients is a deficit in the gamma band auditory steady-state response (ASSR). Over the last years, I have developed various models to look at the mechanisms underlying this deficit (see here, here, here) and built a Python framework to automatically validate such models against experimental observations (see here).

Stimulus-specific Adaptation/Mismatch Negativity

Mismatch negativity (MMN) in the auditory occurs when a sequence of standard auditory stimuli is interrupted by a so-called deviant stimulus that differs in certain aspects. Interestingly, MMN is being increasingly recognized as a candidate biomarker for early stages of psychosis. Despite rapid progress in understanding the function of distinct neuronal populations, the neurobiological mechanisms underlying the generation of the MMN remain unknown. There is considerable debate whether the MMN results from a purely passive, feed-forward habituation (also called stimulus-specific adaptation) or from active cortical predicition processes. Furthermore, we still do not know very much about the different cell types that play a role in both, the generation of the MMN potential and the MMN deficits in patients with psychosis. My student Gili, built a biophysically detailed model of primary auditory cortex to explore the differential contributions of passive, bottom-up adaptation and active, top-down prediction processes. She found that both processes contribute to the MMN and that in schizophrenia (a psychotic psychiatric disorder) the respective strength of the contributions of both processes changes. One interpretation could be that schizophrenia manifests as an impaired novelty detection but with an intact habituation.

Synchronization of E-I Networks

Gamma rhythms play a major role in different processes in the brain, such as attention, working memory and sensory processing. The communication-through-coherence (CTC) hypothesis suggests that synchronization in the gamma band is one of the key mechanisms in neuronal communication and counterintuitively noise can have beneficial effects on the communication. Recently, Meng and Riecke showed that synchronization across interacting inhibitory networks (producing gamma rhythm through an ING mechanism) increases while synchronization within these networks decreases when neurons are subject to independent noise. However, experimental and modeling studies point towards an important role of the PING mechanism in the cortex and the established view is that cortico-cortical connections are predominately excitatory. In his master thesis, my student Lucas Rebscher, reproduced the findings in ING networks of adaptive exponential integrate-and-fire (AdEx) neurons and extended the work by showing that the same synchronization mechanism can be observed in interacting gamma rhythms produced by a PING mechanism.

Large-scale Network Deficits in Schizophrenia

Structural and Synaptic Plasticity in Balanced E-I Networks

Termination of Absence Seizures by Cerebellar Input to Thalamocortical Networks

For current open internship/lab rotation/thesis projects see here