Learning How to Read Minds

Magnetic Resonance Imaging (MRI), despite being one of the most pivotal innovations of contemporary medicine, is markedly limited due to its safety, cost, and inability to discern micro-insults within the brain (Glover, 2011). In 1992, scientists introduced functional Magnetic Resonance Imaging (fMRI), a non-invasive technique intended to measure brain activity with unparalleled specificity (Soares, et al., 2016). Due to fMRI development, physicians may now monitor regional variances in blood flow and brain activity, enabling them to truly understand their patient’s overall feelings and functionality (Glover, 2011). 

In essence, fMRI and MRI function similarly; both methods use the body’s natural magnetic properties to produce detailed images (Berger, 2002). Hydrogen nuclei, due to their magnetic properties and abundance in the body, prove to be ideal targets for fMRI (Jensen, 2014). In the presence of a strong magnetic field, the random and intrinsic spin of hydrogen atoms become aligned, creating a magnetic vector oriented along the axis of the fMRI scanner (Berger, 2002; Jensen, 2014). When additional energy in the form of radio waves is administered, the vector is deflected (Berger, 2002). As the radiofrequency source is switched off, nuclei return to their resting state, emitting various intensities of radio waves that are integrated into comprehensive cross-sectional images (Berger, 2002). This process is illustrated in Figure 1.

Figure 1: Hydrogen proton responses to magnetic fields. A) depicts a water molecule’s structure, containing two hydrogen protons (red circles). Hydrogen protons act like a magnet, containing one positive charge spinning on its axis (blue dotted line). B) portrays the randomized vector (blue arrow) alignment of hydrogen protons under no magnetic field. In the presence of the fMRI’s magnetic field (large black arrow), most hydrogen protons’ axes align to create a magnetic vector that an fMRI can measure. C) depicts hydrogen proton behaviour with radiofrequency (RF) waves. The magnetic vector is deflected and the protons absorb energy. When the RF waves are turned off, the protons return to a resting state and emit RF waves (Broadhouse, 2019).

Although fMRI and MRI are both valuable diagnostic tools, MRI only pictures anatomical structure and imparts no information about function (Vincent, et al., 2008). Studying function is imperative for many clinical conditions including bipolar disorder, where structurally the brain appears normal, yet symptoms are identified from behaviour (Vincent, et al., 2008; Demirci and Calhoun, 2009). fMRI detects function through neuronal activity using the Blood Oxygen Level Dependent (BOLD) signal (Demirci and Calhoun, 2009). By measuring the dynamics of cerebral blood flow, BOLD contrast examines the underlying physiology that may result in a psychiatric disorder (Demirci and Calhoun, 2009). 

The basis of BOLD imaging is grounded in the fundamental understanding that neuronal activity requires oxygen (Vincent, et al., 2008). Therefore, metabolically active regions have higher proportions of oxygenated hemoglobin (OxyHb) to deoxygenated hemoglobin (deOxyHb) than surrounding latent tissue (Vincent, et al., 2008). However, as neuronal activity increases, OxyHb increases beyond metabolic demand, resulting in the decrease of deOxyHb concentration within tissues (Gore, 2003). This decrease directly influences the ability to image function due to OxyHb and deOxyHb having different magnetic qualities (Vincent, et al., 2008; Gore, 2003). 

Structurally, OxyHb unlike deOxyHb, is found to have no unpaired electrons and is classified as weakly diamagnetic (Pauling and Coryell, 1936). However, when OxyHb becomes deOxyHb, four unpaired electrons per heme molecule are exposed, creating a paramagnetic molecule (Pauling and Coryell, 1936). As seen in Figure 2, when OxyHb replaces deOxyHB within neuronally active tissue, distortion within the local magnetic environment decreases (Gore, 2003). This results in greater field uniformity, enhancing image intensity, and allowing researchers to monitor real-time activity (Pauling and Coryell, 1936).

Figure 2: Schematic of BOLD signal in fMRI. OxyHb (pink cells), due to being diamagnetic, have a negligible interaction with the fMRI’s applied magnetic field. As a result, imaging OxyHb creates a magnetically uniform image with no distortions. fMRI signals within neurally active regions of the brain will therefore have higher contrast and be easier to view. deOxyHb (blue cells), are paramagnetic and are influenced by a magnetic field. Imaging deOxyHb will result in distortion of the magnetic field and cause the fMRI signal to decay faster. Using foundational knowledge of magnetism, physicians can accurately image the brain’s structure and function (Gore, 2003). 

fMRI currently has a small, yet burgeoning role in clinical neuroimaging. Applications of fMRI include early diagnosis of psychiatric disease, predicting treatment response, and informing early treatment approaches. The ability to monitor neuronal activity can ultimately aid in the personalization of therapies, development of drugs, and our understanding of various disorders (Orringer, Vago and Golby, 2012). 

Beyond a shadow of a doubt, fMRI has proven to be one of the most powerful tools in modern-day medicine. By offering insight into brain activity, fMRI has heralded a new age of imaging in neuroscience. With further research into fMRI, we can acquire additional information regarding the onset of cognitive disorders and provide more effective treatment for all patients. 

References:

Berger, A., 2002. Magnetic resonance imaging. BMJ, 324(7328), p.35. https://doi.org/10.1136/bmj.324.7328.35.

Broadhouse, K.M., 2019. The Physics of MRI and How We Use It to Reveal the Mysteries of the Mind. Front. Young Minds, 7, p.23. https://doi.org/10.3389/frym.2019.00023.

Demirci, O. and Calhoun, V.D., 2009. Functional Magnetic Resonance Imaging – Implications for Detection of Schizophrenia. Eur Neurol Rev., 4(2), pp.103–106.

Glover, G.H., 2011. Overview of Functional Magnetic Resonance Imaging. Neurosurg Clin N Am, 22(2), pp.133–139. https://doi.org/10.1016/j.nec.2010.11.001.

Gore, J.C., 2003. Principles and practice of functional MRI of the human brain. J Clin Invest, 112(1), pp.4–9. https://doi.org/10.1172/JCI19010.

Jensen, E.C., 2014. Technical Review, Types of Imaging, Part 4—Magnetic Resonance Imaging. The Anatomical Record, 297(6), pp.973–978. https://doi.org/10.1002/ar.22927.

Orringer, D., Vago, D.R. and Golby, A.J., 2012. Clinical Applications and Future Directions of Functional MRI. Semin Neurol., 32(4), pp.466–475. https://doi.org/10.1055/s-0032-1331816.

Pauling, L. and Coryell, C.D., 1936. The Magnetic Properties and Structure of Hemoglobin, Oxyhemoglobin and Carbonmonoxyhemoglobin. Proc. N. A. S., 22, pp.210–216.

Soares, J.M., Magalhães, R., Moreira, P.S., Sousa, A., Ganz, E., Sampaio, A., Alves, V., Marques, P. and Sousa, N., 2016. A Hitchhiker’s Guide to Functional Magnetic Resonance Imaging. Frontiers in Neuroscience, 10, pp.1–35. https://doi.org/10.3389/fnins.2016.00515.

Vincent, K., Moore, J., Kennedy, S. and Tracey, I., 2008. Blood oxygenation level dependent functional magnetic resonance imaging: current and potential uses in obstetrics and gynaecology. BJOG, 116(2), pp.240–246. https://doi.org/10.1111/j.1471-0528.2008.01993.x.


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