Default Mode Network

1
Default Mode Network

• David Jones
• Georgetown University Department of Medicine

2
Neuromodulators, Neurotransmitters, and Neural
Ensembles

• Dopamine and Schizophrenia
• Hypofrontality on fMRI
• DMN, Smell, Memory

3
Default Mode Network
4
Blood Oxygen Level Dependent (BOLD) fMRI

• Diamagnetic, Paramagnetic, and Ferromagnetic
• Deoxyhemoglobin is paramagnetic
• Oxyhemoglobin is diamagnetic
• Field Inhomogeneities

5
Hemodynamic Response Function
6
BOLD Excitation vs. Inhibition

• Recent studies into the relative metabolic demand
  of inhibition and excitation and their effect on
  BOLD signal have concluded that inhibition is far
  less metabolically demanding than excitation
  (Waldvogel et al).

7
Acetylcholine

• Studies have convincingly shown that with
  administration of physostigmine (an
  acetylcholinesterase inhibitor) to healthy
  controls and Alzheimers Disease patients, there
  is a decrement in brain glucose consumption as
  measured by PET scanning after administration of
  isotope labeled glucose (Blin et al).
• Other studies showed a decrease in rCBF, using
  isotope labeled water and PET scanning, with
  administration of physostigmine (Furey et al).
• BOLD deactivations with physostigmine
  administration

8
Acetylcholine and Executive Function

• The role that acetylcholine plays in different
  executive functions is not precisely known.
• However, it has been most convincingly associated
  with attention, perceptual discrimination,
  spatial processing, and memory encoding.

9
How can I look at the DMN and acetylcholine?

• Chemical Shift Imaging another type of fMRI that
  can look at molecules.
• Signal acquisition times on the order of hours
• New Technique SENSE-PEPSI can obtain data on the
  order of seconds.
• Correlation Between BOLD Deactivations and
  Acetylcholine Neurotransmission as Measured by
  Change in Choline Peak Obtained Via SENSE-PEPSI
  An Event-Related fMRI Feasibility Study

10
Thanks

• My mentor Dr. John VanMeter, the Georgetown
  Center for Functional and Molecular Imaging, and
  the GUMC General Clinical Research Center

11
References

• Waldvogel, D., van Gelderen, P., Muellbacher, W.,
  Ziemann, U., Immisch, I., Hallett, M. 2000 The
  relative metabolic demand of inhibition and
  excitation. Nature 406, 995-998.
• Furey, M.L., Pietrini, P., Haxby, J.V.,
  Alexander, G.E., Lee, H.C., VanMeter, J., Grady,
  C.L., Shelty, S.I., Rapoport, S.I., Schapiro,
  M.B., Freo, U. 1997 Cholinergic stimulation
  alters performance and task-specific regional
  cerebral blood flow during working memory. PNAS
  94, 6512-6516.