The Sonification of Human EEG and other Biomedical Data. Part 3

Transcription

1 The Sonification of Human EEG and other Biomedical Data Part 3

2 The Human EEG A data source for the sonification of cerebral dynamics

3 The Human EEG - Outline Electric brain signals Continuous recording with electrodes Neurophysiologic basis of the signals Prominent EEG rhythms Epileptic pathologies as found in EEG

4 The EEG Electrodes on the scalp pick up local field potentials These potentials stem from electric activity of nerve cells in the human cortex. Changes in electric potential are caused by selective ion currents across nerve cell membranes.

5 Action potentials and field potentials Figure from: S. Zschocke, Klinische Elektroenzephalographie, Springer Verlag, Berlin, 2002.

6 Cortex The human cortex is divided into two hemispheres Each hemisphere can be subdivided into functional areas The standard distribution of EEG electrodes tries to map these areas

7 Standard system Specifies the position of electrodes relative to anatomic landmarks like nose and ears. 6 zones in anterior-posterior direction: frontopolar, frontal, central, parietal, temporal and occipital Left hemispheric, central, right-hemispheric Reference electrodes at ear or mastoid

8 Schematic Electrode Placement system Figure from: S. Zschocke, Klinische Elektroenzephalographie, Springer Verlag, Berlin, 2002.

9 Topographic Electrode Placement Figure from: S. Zschocke, Klinische Elektroenzephalographie, Springer Verlag, Berlin, 2002.

10 The EEG Reference A potential is given as the difference between the magnetic field in two points A constant field reference is not available on the human body The choice of reference determines the quality of the signal Each problem requires individual reference considerations

11 Choice of Reference Ear lobe (A1 and/or) A2 Interhemispheric mean (e.g. F3+F4)/2 Bipolar montage (e.g. Fz-Cz) Source derivation (Hjorth or Laplace)

12 Comparison of differently referenced signals Figure from: S. Zschocke, Klinische Elektroenzephalographie, Springer Verlag, Berlin, 2002.

13 And here is what you get:

14 And only after selecting and filtering: Sleep spindle Focal activity Transition to seizure

15 Neural field potentials Field potential of neurons due to ionic current flow Axonal contribution negligible Dendritic and somatic contribution substantial

16 Cortical Field Potentials Activating and inhibitory sources Dendritic and somatic parts of pyramidal neurons are most significant Glial cells enhance But only surface potentials contribute to EEG

17 Cortical Field Potentials Single neuron s contribution are tiny Synchronized activity required Field can be activating (negative) or inhibitory (positive) Strength and sign of contribution depends on orientation of dipole source

18 Cortical dipoles on the scalp Figure from: S. Zschocke, Klinische Elektroenzephalographie, Springer Verlag, Berlin, 2002.

19 EEG patterns - the major rhythms From: Adult Brain Atlas

20 Resting EEG P3 P4 Pz O1 O2 P3 P4 Pz O1 O2 Compare Regularity, Frequency, Synchrony

21 Routine Visualization 2D and pseudo-3d topographic mapping (normally with voltages, but also with frequency band powers)

22 Spatial Distribution of α-rhythm Posterior dominance Figure from: S. Zschocke, Klinische Elektroenzephalographie, Springer Verlag, Berlin, 2002.

23 Origin of α-rhythm Rhythm generator in the thalamus Drives visual cortex Stabilization by feedback mechanism Stability across subjects From:

24 Neurophysiological Evidence: Thalamo-Cortical Rhythm in Brain Slices

25 Clinical Application: EEG Pathologies Dynamic Pathologies Distinguish steady background from shortlived transients Classification of Patterns (Objects)

26 Epilepsy is the Prototype Dynamic Disease First report by Hans Berger, 1933 Characteristic rhythms first categorized by Lennox, Frederic and Erna Gibbs, and others Transient Nature

27 The Absence Seizure (Petit Mal) 60 secs F3 F4 O1 O2 T5 T6

28 Absence Seizure 20 sec F3 F4 O1 O2 T5 T6

29 Focal (partial) Seizure Figure from: S. Zschocke, Klinische Elektroenzephalographie, Springer Verlag, Berlin, 2002.

30 Focal (partial) Seizure 2 Figure from: S. Zschocke, Klinische Elektroenzephalographie, Springer Verlag, Berlin, 2002.

31 The epileptic EEG spike is due to a neural burst Figure from: S. Zschocke, Klinische Elektroenzephalographie, Springer Verlag, Berlin, 2002.

32 Likely Generation of SW Discharge Figure from: S. Zschocke, Klinische Elektroenzephalographie, Springer Verlag, Berlin, 2002.

33 Other registrations of Epileptic EEG Intracranial Measurements (Spontaneous) - Depth electrodes - Cortical Grids (ECoG)

34 Intracranial Recordings Essentially these data allow the same treatment as surface data Figure from: S. Zschocke, Klinische Elektroenzephalographie, Springer Verlag, Berlin, 2002.

35 Interaction possible Both surface EEG and intracranial recordings allow on-line processing and feedback applications Allows communication with LIS patients and therapy for drugresistent epilepsies But use of auditory feedback has been rather primitive so far

36 Auditory Feedback: POSER Multi-feature extraction Combination of sonification techniques Interaction with sonification parameters