Spontaneous Spontaneous activity in the brainactivity 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

•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.

NatureNature, 2007., 2007.

Intrinsic functional architecture in the anaesthetized monkey

brain.

methods

• Macaque monkeys

• Anasthezia done by 0.8-1.5% 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 XOculomotor

Oculomotor XOculomotor

Oculomotor X

Somatomotor

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

ventral dorsal

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 cortex R 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, 2001. 98(2): p. 676-82.

• 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, 2003. 100(1): p. 253-8.

• Gusnard, D.A., and M.E. Raichle, Searching for a baseline: functional imaging and the resting human brain. Nat Rev Neurosci, 2001.2(10): p. 685-94.

• Fox, M.D. and M.E. Raichle, Spontaneous fluctuations in brain activity observed with functional magnetic resonance imaging. Nat Rev Neurosci, 2007. 8(9): p. 700-11.