Spontaneous activity in the brain Eti Ben Simon Imaging Seminar 2008

spontaneous activity Usually we explore brain activity in response to a certain task Yet most of the brain’s energy is devoted to ongoing activity not associated to a specific task The brain uses 20% of the body’s energy of which less than 5% are task related increases Gusnard, D.A., and M.E. Raichle,. Nat Rev Neurosci, 2001 Fox, M.D. and M.E. Raichle, Nat Rev Neurosci, 2007;

Spontaneous neural activity is defined as activity present even in absence of a task or a stimuli Usually extracted when subjects are at rest during fixation What is spontaneous activity

Functional connectivity in motor cortex Arieli using optic imaging showed that spontaneous ongoing activity can explain the large variability in evoked responses. Previous work on spontaneous activity Dynamics of Ongoing Activity: Explanation of the Large Variability in Evoked Cortical Responses,Arieli A. et al,Science 1996 Measured response Predicted response Pre-stimulus Ongoing activity Averaged response Bharat Biswal, F. Zerrin Yetkin, Victor M. Haughton, James S. Hyde TI: Functional connectivity in the motor cortex of resting human brain using echo- planar mri SO: Magnetic Resonance in Medicine Biswal B., F. Zerrin Yetkin, Victor M. Haughton, James S. Hyde Functional connectivity in the motor cortex of resting human brain using echo-planar mri, Magnetic Resonance in Medicine,1995

Main question: Whether spontaneous activity is related to conscious mental activity? Vincent, J. L.,Patel, G. H.,Fox, M. D.,Snyder, A. Z.,Baker, J. T.,Van Essen, D. C.,Zempel, J. M.,Snyder, L. H.,Corbetta, M.,Raichle, M. E. Nature, Nature, Intrinsic functional architecture in the anaesthetized monkey brain.

methods Macaque monkeys Anasthezia done by % isoflorune 15 minutes acquisition (3T magnet)

Methods Correlation of BOLD fluctuations time course averaged from a seed ROI with the time course of each voxel in the brain Fox, M.D. and M.E. Raichle, Nat Rev Neurosci, 2007

Spontaneous BOLD correlations Results from anesthesized monkeys (N=8)

Temporal and spatial correlation of pairs of ROI Oculomotor X Oculomotor Oculomotor X Somatomotor

Comparison of task evoked activity and spontaneous activity Spontaneous BOLD correlation in oculomotor system ( 8 anesthetized monkeys) BOLD correlation to saccadic eye movements task (avg of 2 awake monkeys) Retrograde tracer from LIP

spontaneous activity reveal functional architecture Spontaneous BOLD correlation are topographically organized in the visual cortex (8 anesthetized monkeys) Seed ROI Seed ventraldorsal

Default Brain Activated at rest, deactivated at task performance assumed to be unique to humans Includes : dmPFC, vmPFC, RTS Gusnard, D.A., and M.E. Raichle,. Nat Rev Neurosci, 2001

Default monkey brain?

conclusions Cortical systems associated with task performance are also evident in spontaneous BOLD fluctuations (even in anesthesia) Coherent spontaneous BOLD fluctuations is not exclusively a reflection of conscious mental activity Might reflect a more intrinsic property of functional brain organization  supports the idea that the brain is governed primarily by internal dynamics

correlated between functional systems and are not noise relate to neuro-anatomical systems Exists in sleep and anaesthesia Might account for inter trial variability Spontaneous activity so far Fox, M.D. and M.E. Raichle, Nat Rev Neurosci, 2007 L motor cortexR motor cortex

Future work Compare spontaneous BOLD activity between groups Use combined studies to reach better temporal and spatial scales such as iEEG and BOLD or to explore functional connectivity

Articles : Raichle, M.E., et al., A default mode of brain function. Proc Natl Acad Sci USA, (2): p Greicius, M.D., et al., Functional connectivity in the resting brain: a network analysis of the default mode hypothesis. Proc Natl Acad Sci U S A, (1): p Gusnard, D.A., and M.E. Raichle, Searching for a baseline: functional imaging and the resting human brain. Nat Rev Neurosci, (10): p Fox, M.D. and M.E. Raichle, Spontaneous fluctuations in brain activity observed with functional magnetic resonance imaging. Nat Rev Neurosci, (9): p