Samora Okujeni

University of Freiburg | Albert-Ludwigs-Universität Freiburg · Department of Microsystems Engineering (IMTEK)

Numerous studies suggest that biological neuronal networks self-organize towards a critical state with stable recruitment dynamics. Individual neurons would then statistically activate exactly one further neuron during activity cascades termed neuronal avalanches. Yet, it is unclear if and how this can be reconciled with the explosive recruitment d...

The 22q11.2 deletion has been identified as a risk factor for multiple neurodevelopmental disorders. Behavioral and cognitive impairments are common among carriers of the 22q11.2 deletion. Parvalbumin expressing (PV+) interneurons provide perisomatic inhibition of excitatory neuronal circuits through GABAA receptors, and a deficit of PV+ inhibitory...

The spatial distribution of neurons and activity-dependent neurite outgrowth shape long-range interaction, recurrent local connectivity and the modularity in neuronal networks. We investigated how this mesoscale architecture develops by interaction of neurite outgrowth, cell migration and activity in cultured networks of rat cortical neurons and sh...

The mesoscale architecture of neuronal networks strongly influences the initiation of spontaneous activity and its pathways of propagation. Spontaneous activity has been studied extensively in networks of cultured cortical neurons that generate complex yet reproducible patterns of synchronous bursting events that resemble the activity dynamics in d...

Spontaneous activity in the absence of external input, including propagating waves of activity, is a robust feature of neuronal networks in vivo and in vitro. The neurophysiological and anatomical requirements for initiation and persistence of such activity, however, are poorly understood, as is their role in the function of neuronal networks. Comp...

Electrical stimulation of the brain is increasingly used to alleviate the symptoms of a range of neurological disorders and as a means to artificially inject information into neural circuits in neuroprosthetic applications. Machine learning has been proposed to find optimal stimulation settings autonomously. However, this approach is impeded by the...

Motivation Electrical stimulation of the brain is increasingly used as a strategy to alleviate the symptoms of a range of neurological disorders, and as a possible means to artificially inject information into neural circuits, e.g. towards bidirectional neural prostheses [1]. Conventionally, stimulation of neuronal networks explicitly or implicitly...

Penetrating microelectrode probes offer the opportunity to precisely monitor neuronal signals over several months. After the experimental end point, histological methods are used to analyze the tissue and to correlate recorded signals to histological findings. However, accurate retroactive tracing of the position of individual microelectrodes is cu...

Variable responses of neuronal networks to repeated sensory or electrical stimuli reflect the interaction of the stimulus' response with ongoing activity in the brain and its modulation by adaptive mechanisms such as cognitive context, network state or cellular excitability and synaptic transmission capability. Here, we focus on reliability, length...

Cultured neuronal networks are an interesting experimental model in which neurons are freed from cortical architecture and plated on microelectrode arrays (MEA). Present in their dynamics are periods of strongly synchronized spiking by the network, termed 'bursting', whose role is not understood but dominates network dynamics and, due to its resist...

The emergence of spontaneous bursting events in developing neuronal networks likely depends on the evolving network connectivity. Theoretical models have shown that hierarchical network structures embedding clusters of strongly inter-connected neurons are optimal for initiating and sustaining spontaneous activity [1]. It is conceivable that activit...

In this work we study the excitatory AMPA, and NMDA, and inhibitory GABA A receptor mediated dynamical changes in neuronal networks of neonatal rat cortex in vitro. Extracellular network-wide activity was recorded with 59 planar electrodes simultaneously under different pharmacological conditions. We analyzed the changes of overall network activity...

Derivation of the steady state firing rate R*. (0.03 MB PDF)

Derivation of the nullcline of the model. (0.03 MB PDF)

Recently evidence has accumulated that many neural networks exhibit self-organized criticality. In this state, activity is similar across temporal scales and this is beneficial with respect to information flow. If subcritical, activity can die out, if supercritical epileptiform patterns may occur. Little is known about how developing networks will...

Self-organized criticality (SOC) [1] was first described inneuronal cell cultures by Beggs and Plenz [2]. Neuronalnetworks being in a critical state produce avalanche-likedischarges that are power-law distributed. The assessmentof avalanches in neuronal networks is a new way of look-ing at neuronal activities apart from bursts, synchroniza-tion etc...

Complementing single electrode recordings, passive, substrate-integrated thin-film microelectrode arrays (MEAs) have become established tools to investigate spatio-temporal patterns of electrical activity and neuronal interaction in-vitro. In the neurosciences, acute brain slices with accessible and well-preserved neuronal microcircuitry have becom...