Simultaneous measurements of somatosensory evoked AC and near-DC MEG signals

Abstract Magnetoencephalography measurements of somatosensory evoked brain activity taken inside an extremely magnetically shielded room are reported. The massive low frequency shielding in combination with a high sampling rate enabled the simultaneous observation of AC and near-DC effects. Neuronal activation was achieved by repetitive electrostimulation of the right median nerve above motor threshold using repetition rates from 3 Hz to 12 Hz. Stimulation sequences lasted for 10 s and were interspersed with periods of rest of equal length. The recorded magnetic fields, inferred for the N20m and a sustained near-DC component, revealed mainly dipolar patterns with mutually rotated orientations with angles of rotation of 30° and 75°. At the start of the stimulation we observed a fast rise within 100 ms in the evoked magnetic near-DC fields for which a maximum equivalent current dipole strength of 65 nAm was obtained. The sustained fields decayed by a factor of ∼4 to a lower DC-level Bγ with a time constant τ of order of seconds. For 12 Hz repetition rate Bγ was decreased. We suggest that the sustained neuronal activity evoked by repetitive electrostimulation could provide a suitable scheme to realize the direct detection of DC effects of neuronal currents via low field magnetic resonance.

[1]  Gabriel Curio,et al.  On the feasibility of neurocurrent imaging by low-field nuclear magnetic resonance , 2010 .

[2]  Martin Burghoff,et al.  Neuronal current detection with low-field magnetic resonance: simulations and methods. , 2009, Magnetic resonance imaging.

[3]  Gabriel Curio,et al.  Differential infraslow (<0.1 Hz) cortical activations in the affected and unaffected hemispheres from patients with subacute stroke demonstrated by noninvasive DC-magnetoencephalography. , 2009, Stroke.

[4]  Martin Burghoff,et al.  Squid system for meg and low field magnetic resonance , 2009 .

[5]  N. Logothetis,et al.  Neurophysiology of the BOLD fMRI Signal in Awake Monkeys , 2008, Current Biology.

[6]  J. Mosher,et al.  Microtesla MRI of the human brain combined with MEG. , 2007, Journal of magnetic resonance.

[7]  John Clarke,et al.  SQUID-detected magnetic resonance imaging in microtesla fields. , 2007, Annual review of biomedical engineering.

[8]  Bruno Maraviglia,et al.  Challenges for detection of neuronal currents by MRI. , 2006, Magnetic resonance imaging.

[9]  Gabriel Curio,et al.  Tonic neuronal activation during simple and complex finger movements analyzed by DC-magnetoencephalography , 2006, Neuroscience Letters.

[10]  Alex I. Braginski,et al.  Applications of SQUIDs and SQUID systems , 2006 .

[11]  Dietmar Drung,et al.  dc Magnetoencephalography: Direct measurement in a magnetically extremely-well shielded room , 2004 .

[12]  B. Mackert.  The discovery of slowness--recent progress in DC-MEG research. , 2004, Neurology & clinical neurophysiology : NCN.

[13]  Dietmar Drung,et al.  High-Tc and low-Tc dc SQUID electronics , 2003 .

[14]  Y. Haruta,et al.  Contribution of primary somatosensory area 3b to somatic cognition: a neuromagnetic study , 2002, Neuroreport.

[15]  G Curio,et al.  Non-invasive single-trial monitoring of human movement-related brain activation based on DC-magnetoencephalography , 2001, Neuroreport.

[16]  Riitta Hari,et al.  Sustained Activation of the Human SII Cortices by Stimulus Trains , 2001, NeuroImage.

[17]  Gabriel Curio,et al.  Non-invasive long-term recordings of cortical ‘direct current’ (DC–) activity in humans using magnetoencephalography , 1999, Neuroscience Letters.

[18]  G. Wübbeler,et al.  SQUID measurements of human nerve and muscle near-DC injury-currents using a mechanical modulation o , 1999 .

[19]  B. Ross,et al.  The Auditory Evoked “Off” Response: Sources and Comparison with the"On" and the “Sustained” Responses , 1996, Ear and hearing.

[20]  K D Wolff,et al.  Non-invasive neuromagnetic monitoring of nerve and muscle injury currents. , 1993, Electroencephalography and clinical neurophysiology.

[21]  R. Ilmoniemi,et al.  Magnetoencephalography-theory, instrumentation, and applications to noninvasive studies of the working human brain , 1993 .

[22]  E.-J. Speckmann,et al.  Introduction of the neurophysiological basis of the EEG and DC potentials , 1993 .

[23]  J. Sarvas.  Basic mathematical and electromagnetic concepts of the biomagnetic inverse problem. , 1987, Physics in medicine and biology.

[24]  A. Walker.  Electroencephalography, Basic Principles, Clinical Applications and Related Fields , 1982 .