Ole Jensen 08/06/2005
F.C. Donders Centre for Cognitive Neuroimaging
New Perspectives on Rhythmic Brain Activity
Ole Jensen
F.C. Donders Centre for Cognitive Neuroimaging
Ole Jensen 08/06/2005
F.C. Donders Centre for Cognitive Neuroimaging
Spontaneous Oscillatory Activity
Ole Jensen 08/06/2005
F.C. Donders Centre for Cognitive Neuroimaging
+ + ... =
Calculating power spectra
Jensen and Vanni (2002) Neuroimage 15:568
Identifying oscillatory sources by minimum current estimates
Number of Grid Points (~1000)>
Number of Sensors (~100)
Constraint:
Minimize the total currentmin || q ||
Sources of Sensory-Motor Beta ActivityIdentified by MCEfd
Jensen et al. (2005) Neuroimage 26:347-355
Ole Jensen 08/06/2005
F.C. Donders Centre for Cognitive Neuroimaging
Evoked and Induced Responses
evoked induced
trial 1
trial 2
trial 3
average
trial n
. . .
F.C. Donders Centre for Cognitive Neuroimaging
Ole Jensen
Ole Jensen 08/06/2005
F.C. Donders Centre for Cognitive Neuroimaging
Evoked and Induced Responses
evoked induced
trial 1
trial 2
trial 3
average
trial n
. . .
F.C. Donders Centre for Cognitive Neuroimaging
Ole Jensen
Ole Jensen 08/06/2005
F.C. Donders Centre for Cognitive Neuroimaging
Characterizing Induced Oscillatory Activity Using Wavelets
Ole Jensen 08/06/2005
F.C. Donders Centre for Cognitive Neuroimaging
Example:
Evoked fields and beta oscillations in a “N400” language comprehension task
Ole Jensen 08/06/2005
F.C. Donders Centre for Cognitive Neuroimaging
Time-Frequency Representations(Planar gradient)
F.C. Donders Centre for Cognitive Neuroimaging
Incongruentsentences:
Ole Jensen
ERFs and Oscillatory Responses Provide Complementary Information
TFRs (beta rebound):ERF (N400m):
15 – 22 Hz0.3 – 1.5 s
0.3 – 0.6 s
F.C. Donders Centre for Cognitive Neuroimaging
Ole Jensen 08/06/2005
F.C. Donders Centre for Cognitive Neuroimaging
Identifying sources using beamforming/spatial filtering
• Linearly Constrained Minimum Variance (LCMV)
• Synthetic Aperture Magnetometry (SAM)
• Dynamical Imaging of Coherence Sources (DICS)
Spatial filtering
The measured field at sensor x(t) given source yr (t) and forward model H(r)
x(t) = H(r) yr (t) + n(t)
H1
H2
H3
H4
H5
x1(t)
x2(t)
x3(t)
x4(t)
x5(t)
yr(t)
sr(t) = Σi=1:n
w(r) x(t)
h1
h2
h3
h4
h5
yr
x1(t)x2(t)
x3(t)
x4(t)
x5(t)
w1r
w2r
w3r
w4r
w5r
sr (t) = w(r)T x(t)
“Strength“ of activity at location r:
sr (t) = w(r)T x(t)
Ole Jensen 08/06/2005
F.C. Donders Centre for Cognitive Neuroimaging
Scanning ....
w(r) = [HT(r) Cov-1(x) H(r)]-1 HT(r) Cov-1(x)
w(r)
Ole Jensen 08/06/2005
F.C. Donders Centre for Cognitive Neuroimaging
Sources of The Beta Increase IdentifiedUsing a Beamformer Technique
Ole Jensen 08/06/2005
F.C. Donders Centre for Cognitive Neuroimaging
Summary
• Oscillatory activity– Spontaneous/ongoing
– Induced/event related
– Modulated by behavior
• Characterization in time and frequency– Power spectra
– Wavelets, FFT-based spectrogram, multitapers
• Identification of sources– Current estimates (MCE/MNE)
– Beamforming techniques
Ole Jensen 08/06/2005
F.C. Donders Centre for Cognitive Neuroimaging
Suggested reading
MEG/oscillations general:• Hari R (2005) Magnetoencephalography in Clinical Neurophysiological Assessment of Human Cortical Functions. In
Electroencephalography: Basic Principles, Clinical Applications, and Related Fields (eds. E. Niedermeyer F. Lopes da Silva). 5th edition. Lippincott Williams & Wilkins
• Hari R, Salmelin R. (1997) Human cortical oscillations: a neuromagnetic view through the skull. Trends Neurosci. 1997 Jan;20(1):44-9.
• Tallon-Baudry C, Bertrand O. (1999) Oscillatory gamma activity in humans and its role in object representation. Trends Cogn Sci. 3:151-162.
• Varela F, Lachaux JP, Rodriguez E, Martinerie (2001) The brainweb: phase synchronization and large-scale integration. Nat Rev Neurosci. 2:229-39.
Power spectra + wavelets• Challis RE, Kitney RI. SE. (1991) The power spectrum and coherence function. Medical & Biological Engineering and Computing.
225-241• Steven W. Smith (1997) The Scientist and Engineer's Guide to Digital Signal Processing California Technical Publishing. http://• Sinkkonen J, Tiitinen H, Naatanen R.(1995) Gabor filters: an informative way for analysing event-related brain activity. J Neurosci
Methods. 56:99-104. • Tallon-Baudry C, Bertrand O. (1999) Oscillatory gamma activity in humans and its role in object representation. Trends Cogn Sci.
3:151-162. Localizing oscillatory sources• Liljestrom, M., Kujala, J., Jensen, O., and Salmelin, R. (2005). Neuromagnetic localization of rhythmic activity in the human brain: a
comparison of three methods. Neuroimage 25:734-745. • Jensen, O. and Vanni, S. (2002) A new method to identify multiple sources of oscillatory activity from magnetoencephalographic
data. Neuroimage 15:568-574 • Vrba J, Robinson SE. (2001) Signal processing in magnetoencephalography. Methods. 25:249-71 Gross J, Kujala J, Hamalainen M,
Timmermann L, Schnitzler A, Salmelin R. (2001) Dynamic imaging of coherent sources: Studying neural interactions in the human brain. Proc Natl Acad Sci U S A. 98(2):694-9.
• Hillebrand A, Singh KD, Holliday IE, Furlong PL, Barnes GR. (2005) Hum Brain Mapp. 25:199-211. A new approach to neuroimaging with magnetoencephalography.