Spatio-temporal structure of thalamically evoked activity in the barrel cortex

The barrel cortex integrates incoming information conveyed via thalamocortical pathways and ongoing activity thereby extracting the relevant details from spatio-temporal dynamic stimuli that carry information about the environment. In the course of this, the cortical response to the incoming information depends on the actual state of activity of the network and the state of activity is influenced by the incoming information. <br>In this project, I investigated how the pattern of activity in the barrel cortex is shaped by incoming sensory information, and how successive stimuli interact with each other. I used rat thalamocortical slices preserving the functional coupling between the ventrobasal thalamic nucleus and the ‘barrel’ cortex. Local field potentials (LFP) and spike activity were recorded in the ‘barrel’ cortex with multi-electrode arrays, while electrical stimulation of the thalamocortical pathway simulated incoming sensory information. <br>Glutamatergic responses to thalamocortical stimulation spanned multiple barrels starting 1–2 ms after the first fibre volley in the input layers IV and Vb and afterwards spread to supra- and infragranular layers. Glutamatergic responses were immediately followed by feed-forward inhibition. A model based on common biophysical assumptions reproduced the LFP waveform showing that monosynaptic glutamatergic activation was followed by disynaptic inhibition. This inhibition often led to rebound activity manifested as population EPSPs (pEPSP) and stimulus locked spike activity (mostly in IV). Spike activity was also found locked to the first pEPSP. <br>Besides paired-pulse depression on the short time scale, the first stimulus was also able to change the network state on a longer time scale, resulting in a different type of response to the second stimulus: long lasting and highly variable LFP fluctuations or ensemble activity starting ~10–100 ms poststimulus time and lasting for several hundred milliseconds. Ensemble activity was best induced with an intra-pair interval of 20 ms and an inter-pair interval of 20 s. The observation that the ensemble activity was induced less effectively by using a shorter inter-pair interval of 5 s is a very interesting finding as it indicates that network properties are changed on the time scale of several seconds by such stimuli. During application of bicuculline, ensemble activity was blocked, instead epileptiform activity appeared with ten-fold higher amplitudes in the LFP. The observations that ensemble activity had a much smaller amplitude than epileptiform activity, that the on- and offsets of ensemble activity were variable and that ensemble activity showed highly variable fluctuations of the waveform over trials, led to the hypothesis that ensemble activity locally and dynamically recruits neurones into changing ensembles of synchronous activity. It might use the same mechanisms as ongoing or background activity in vivo.

Author dc:creator

• Schlabrendorff, Carl-Ludwig von

Contributors dc:contributor

• Aertsen, Ad

• barrel cortex
• thalamus
• in vitro
• micro-electrode arrays
• rat

Repository record source_url

https://freidok.uni-freiburg.de/data/1262

OAI identifier oai:identifier

oai:freidok.uni-freiburg.de:1262