2The brain never rests!Brain takes up 20% of the metabolites in the body during rest.
3Energy costsEnergy consumption measured with PET (radioactive glucose consumption) during 4 conditions.Which is rest and which is task?
4Brain is always at max power: similar costs in all conditions Energy costsBrain is always at max power: similar costs in all conditions
5Energy costs Energy cost breakdown for running the cortex. Most of the energy is spent on neural signaling.
6Information encoding Given that energy consumption is almost constant: Only relatively smallpopulations of neuronsrespond strongly at anygiven time.Relatively local, transientchanges in neuralactivity represent stimulievoked responses.Hence the importance of:Attention and neurovascular coupling
7Brain is never static!Connected neural populations tend to synchronize and oscillate together.
8EEG Alpha (10 Hz) Close eyes Over occipital electrodes. Different time scales of synchronization
9Slow changes Similar fluctuations in fMRI signal during rest Nir Y., Neuroimage (2006)
10Structure of rest activity Spontaneous neural activity during rest and sleep may be random over time, but it’s not random over space.Large neural populations are synchronized.What are the characteristics of this activity?How can we study them? No experimental structure?Are there differences between rest, sleep, anesthesia?
12Local spatial structure Many occurrences of strong correlation between spontaneous and evoked columnar maps.
13Local spatial structure Correlation between spontaneous “snapshots” and particular orientation columnar maps.Visual cortex randomly moves from one map to another in the absence of stimulation (relatively quick transitions).
14Large spatial structure Very slow hemodynamic changes over time.Cortical areas with similar functionality (e.g. right and left auditory cortex) show strong and selective correlations.
15Functional connectivity Areas that are connected anatomically because of shared functionality will be active together.In reality this is just correlation – problematic interpretation
16Inter-hemispheric correlations Strongest correlations are between corresponding locations in the two hemispheres
17Default mode systemThree areas that show reduced activity during “external” tasks (e.g. visual, auditory, somatosensory stimulation)
18Default mode system at rest “Intrinsic” ROI“Extrinsic” ROIIs the brain separated into two general antagonistic networks?Measuring default mode system correlations during rest.
19Source of fMRI correlations Several “less interesting “ sources contribute to an fMRI signal. Are they driving correlations during rest?
20Source of fMRI correlations Simultaneous fMRI and electrophysiology:Shmuel et. al. HBM 2008
21Source of fMRI correlations Significant correlations between neural activity and BOLD during rest…
22Source of fMRI correlations Similar inter-hemispheric correlations in epilepsy patientsNir Y., Nat. Neurosci. (2010)
23Source of fMRI correlations Correlations during rest correspond to anatomically connected areas that are commonly active during task.Fox, Nat. Rev. Neurosci. (2007)
24Patient lacking corpus callosum Inter-hemisphericcorrelations disappear after section of corpus callosum.
25Spontaneous and evoked activity There’s a lot of variability in the neural response to the same repeating visual stimulus.Arieli, Science (1996)
26Spontaneous and evoked activity The spontaneous state right before stimulation predicted the amplitude of the response 42 ms later.
27Spontaneous and evoked activity Changing the spatial response pattern in a predictable way.Is the evokedresponse to atrial the sum ofspontaneousand evokedactivity?
28Motor response variability Right hand button press LH ROIFunctionally correlated RH ROIFox, Nat. Neurosci. (2006)
29Motor response variability Subtracting out RH spontaneous activity, allowed reduction of trial by trial evoked response variability.LH responsesRH responses
30Diagnosis by rest scans If resting state correlations represent the functionality of the brain, abnormal correlations may represent abnormal functionality and enable an easy form of diagnosis.Build a distribution of “normal” correlation values and test whether these deviate in particular neurological or psychiatric disorders.
31Alzheimer’s diseaseControlAlheimer’sWeaker resting state correlations between “default mode” network (precuneus area) and hippocampi.Fare comparison?Greicius, PNAS (2004)
32Alzheimer’s disease Direct comparison: Voxels that showed stronger correlation with PPC timecourse in controls versus Alzheimer’s patients.
33CommaPatients in reduced states of awareness show decreased inter-hemispheric correlations.
34Autism1-3 year old children with autism or language delay, during natural sleep.Strong inter-hemispheric correlations are already evident at extremely young ages.
35AutismDecreased inter-hemispheric correlations in language areas
36AutismInter-hemispheric correlation strength predicts language ability and autism symptom severity.
37Rest activity and development Visual system development (e.g. ocular dominance) before birth (i.e. before visual experience)
38Hebbian learning during rest? In the absence of externally evoked responses?
39Different temporal and spatial scales of organization. SummarySpontaneous brain activity is the largest and least understood component of brain function.Different temporal and spatial scales of organization.