• experimental
  
• epidemiological
  

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Medical/biological Study (experimental study)

Simulated MR magnetic field induces steady-state changes in brain dynamics: Implications for interpretation of functional MR studies. med./biol.

PubMed Entry

Journal web site

Aim of study (according to author)
To test the hypothesis that a magnetic field comparable to a field generated during a MR scan produced changes in human brain electrical activity that persisted until the field was removed (called a "presence effect" to distinguish it from evoked potentials).
Background/further details:
Individual subjects (n=22, 9 males, 13 females) served as their own controls. As a positive control a binaural 424 Hz tone was presented.
Following an acclimation period, every subject underwent three blocks of trials: the magnetic field was applied in either the first or third block, as determined randomly from subject to subject. The data from the block where the field was not applied were analyzed as a negative control (sham exposure). The auditory stimulus was applied in the middle block (positive control).

Endpoint

• effects on the neurological system: electrical activity in the brain (EEG)

Exposure
General category: magnetic field, 50/60 Hz (AC), MRI

Field characteristics	Parameters
60 Hz exposure duration: 2 s on - 5 s off - for 560 s	magnetic flux density: 100 µT min value magnetic flux density: 200 µT max value

Exposed system:
human
partial body exposure: coronal plane

Methods
Endpoint/Measurement parameters/Methodology

• effects on the neurological system: electrical activity in the brain (EEG; nonlinear recurrence analysis and linear time averaging analysis)

Main outcome of study (according to author)
Using non-linear recurrence analysis, changes in brain activity lasting 1 sec (the longest interval considered) were found in 21 of 22 subjects. The "presence effect" was not detected using linear analysis and was reversible, as indicated by a return of brain activity to baseline levels in all subjects within 2 seconds of field offset.
The authors suggest that actual MRI magnetic fields produce nonlinear steady-state perturbations of brain dynamical activity. The effect may influence the picture of brain connectivity inferred in some functional MRI studies.

(Study character: medical/biological study, experimental study, full/main study)

Study funded by

• not stated

• Carrubba S et al. (2010): Numerical analysis of recurrence plots to detect effect of...
• Carrubba S et al. (2008): Magnetosensory evoked potentials: consistent nonlinear phenomena.
• Carrubba S et al. (2007): Nonlinear EEG activation evoked by low-strength low-frequency magnetic fields.
• Carrubba S et al. (2007): Evidence of a nonlinear human magnetic sense.
• Carrubba S et al. (2006): Detection of nonlinear event-related potentials.