Informationsverarbeitung im zerebralen Cortex

Transcription

1 Informationsverarbeitung im zerebralen Cortex Thomas Klausberger Dept. Cognitive Neurobiology, Center for Brain Research, Med. Uni. Vienna

2 The hippocampus is a key brain circuit for certain forms of memory Events Places H.M. (Henry Gustav Molaison, ) ( ) After operation this young man could no longer recognize the hospital staff nor find his way to the bathroom, and he seemed to recall nothing of the day-to-day events of his hospital life. ( ) he did not remember the death of a favourite uncle three years previously ( ). The family moved from their old house to a new one a few blocks away on the same street; he still has not learned the new address, though remembering the old one perfectly, nor can he be trusted to find his way home alone. ( ) This patient has even eaten luncheon in front of one of us ( ), a mere half-hour later ( ) he could not remember having eaten luncheon at all. Yet to a casual observer this man seems like a relatively normal individual, since his understanding and reasoning are undiminished. in Scoville and Milner, 1957

3 Nervenzellen codieren Informationen mittels Aktionspotentiale und sind via Synapsen miteinander verbunden

4 Pyramidal cells labelled in vivo by neurobiotin in the rat hippocampal CA1area.

5 Extracellular multi-channel recording in ~60 channels Signal processing is needed to detect action potentials and field oscillatory patterns

6 Tetrodes are used to enable separation of spikes from different cells Tetrode: 4 wires bundled together 1 Local field potentials containing spikes from cells a and b Cell b Cell a Cell a Cell b Clustering procedure is needed to differentiate the waveforms of different cells. This procedure is semi-automatic so far.

7 64-channel probe 20μm 20ms 200μm

8 Feature 1 Clustering: separating multiunit activity into single units 5ms 600Hz-5kHz Plotting the features of each spike (e.g. Amplitude) measured on different electrodes in the tetrode bundle segregates the spikes into clouds ( clusters ). Feature 1

9 Temp (K) Active Probe Encapsulation K MTTF (days) Calculated MTTF Measured MMTF Active probe with 2.5 micron electroplated gold shield Cross section of plated gold film and extrapolated mean time to failure

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11 Czurko et al. Eur. J.Neurosci. 1999

12 Hippocampal Pyramidal cells fire, when a rat runs through a certain place O Keefe, Exp. Neurol., m Red strong firing of a certain pyramidal cell Blue no firing of the same cell Food Cups

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14 Place Cells are stable over long periods of time Distal cues affect firing patterns place field of a single cell place field is stable over time after O Keefe and Nadel, 1978

15 Not only visual information is used for place cell firing. The hippocampus is a high order cortical area. light dark Light back on Place field of a pyramidal cell

16 Different pyramidal cells have distinct place fields. This produces a spatial map of the environment. a Place fields of different place cells in the same environment. The black line shows path of the rat. The red line shows computer prediction based on information of place cell activity. Wilson, McNaughton, Science 1993

17 Cell assemblies: groups of cells that work together in a common (cognitive) task ''cell assembly... a diffuse structure comprising cells in the cortex and diencephalon, capable of acting briefly as a closed system, delivering facilitation to other such systems...'' Donald Hebb (1949) The Organization of Behavior Donald Hebb proposed that when cells repeatedly fire together, they increase their firing-associations with each other and form a cell assembly. Harris, Csicsvari, Hirase, Dragoi and Buzsaki, Nature, 2003

18 Place cells exist also in humans (Eckstrom et al., Nature 2003)

19 The Jennifer Aniston Neuron Quiroga et al., Nature 2005 aniston

20 Attractor Dynamics in the Hippocampal Representation of the Local Environment Wills et al. Science 308, ; 2005

21 The human EEG EEG Brain waves and network oscillations

22 The first EEG recordings in humans by Hans Berger Hans Berger ( ) Recordings of EEG made by Berger Patient of Berger

23 Network oscillations in the cortex are coupled with distinct behaviour Slow Hz slow wave sleep Delta 1-4 Hz slow wave sleep Usual behaviour of rat Theta 4-8 Hz exploration, sensory processing, paradoxical sleep Alpha 9-13 Hz awake inaction Beta Hz sensory processing Gamma Hz exploration, sensory processing paradoxical sleep High Hz immobility, consummatory behaviour, frequency (ripple) slow wave sleep

24 Hippocampal network oscillations predict behaviour navigation still 1 mv 1 sec theta ripples Buzsaki, Neurosci. 1989

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26 Pyramidal cell spikes precess relative to theta wave; phase coding for location Scheme by John O Keefe, University College, London J. O Keefe and M. Recce, Hippocampus, running speed theta cycle marks EEG (field potential) Single pyramidal cell firing (place cell) Place field of the cell 1.5 m (also during REM sleep) Food Cups

27 Theta phase precession The spike timing of place cells relative to theta oscillation encode place on the linear track food food wall wall 1 Spikes fired (single run) O Keefe & Recce, Hippocampus, 1993 Skaggs et al., Hippocampus, 1996

28 trough peak What does phase precession encode for? Phase precession a temporal code for location? Huxter Burgess & O Keefe, Nature, 2003 Repetition of sequences reflecting the position sequence Skaggs et al., Hippocampus, 1996 Dragoi & Buzsaki, Neuron, r f

29 Interference between two distinct oscillators can produce phase precession (O Keefe)

30 Stimulus Intensity Frequency code hypothesis Analog information is coded by changing discharge frequency of neuronal ensembles Frequency code Receptive field (place) Hz Hz Time time

31 Spike phase precession: temporal code Timing of spikes within the theta cycle correlates with spatial position of rat EC theta Spatial position (distance - m) time O Keefe, Recce Hippocampus 1993 Buzsaki, Neuron 2002

32 neurons Frequency coding Temporal coincidence Field time time Delay coding input current subthreshold membrane oscillation d4 d3 d2 d1 time Spatio-temporal coding d5 d4 d3 d2 time

33 The activity of assemblies of pyramidal cells is repeated during REM sleep. Dreaming? (Louie and Wilson, Neuron 2001)

34 (theta) Reverse replay of spatial memory during ripples (Foster and Wilson, Nature 2006) Theta: Ripples: (ripples)

35 Binding theory and gamma oscillations Engel et al., Nat. Rev. Neurosci. 2, (2001)