The Bernstein Center for Computational Neuroscience Freiburg

Announcement for the next
BCCN Seminar
Dr. Fritjof Helmchen
Institut für Hirnforschung

New tools for in vivo studies of population dynamics in the neocortex
Thursday, November 23, 2006
17:15 h
Lecture Hall (ground floor)
BCCN building
Hansastraße 9A
79104 Freiburg
Spatiotemporal activity patterns in three-dimensionally organized cellular networks are fundamental to the function of the nervous system. Recently, new methods for in vivo staining of cell populations with anatomical and functional indicators have been developed. Combined with two-photon microscopy they for example enable studies of network dynamics in the neocortex. In particular, bulk-loading with calcium indicator dye now permits indirect measurements of neural activity based on spike-evoked calcium transients, even with single-spike resolution. In addition, calcium signals in the surrounding astrocytic network and the neuropil can be measured simultaneously. Despite these advances in functional imaging of cell populations, in vivo imaging of population activity so far has been restricted to two dimensions with rather arbitrary subsets of cells in the local 3D network sampled. The reason is that 3D imaging techniques with sufficiently high temporal resolution to resolve spiking activity (>= 10 Hz) have not been available. To overcome this limitation we introduce a novel 3D laser scanning technology for two-photon microscopy that for the first time permits fast fluorescence measurements from several hundred cells distributed in 3D space. The basic idea is to perform a 3D linescan that passes through as many cell bodies as possible. We found that more than 90% of cell somata can be sampled by the scan line within volumes of 250 microns side length (containing on the order of 400 cells). We applied this method to reveal spatiotemporal activity patterns in neuronal and astrocytic networks in rat somatosensory cortex in vivo. Activity was monitored in response to local electrical stimulation and was visualized using 3D visualization software Amira. We are currently applying this technique to reveal whisker-evoked activity patterns in superficial layer 2/3 of identified barrel columns in rat barrel cortex.