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Understanding Brain Imaging

Daniel Lende and Greg Downey run the though-pro­vok­ing Neu­roan­thro­pol­o­gy blog. Daniel also teach­es a class at Uni­ver­si­ty of Notre Dame, and he asked his stu­dents to sub­mit group-based blog posts in lieu of the tra­di­tion­al final essays. He explains more on Why A Final Essay When We Can Do This?.

Below you have a spec­tac­u­lar post writ­ten by 4 of his stu­dents. They show how brain imag­ing is start­ing to pro­vide a win­dow into the plas­tic­i­ty (glos­sary here) of our brains, and how our very own actions impact them. For good and for bad.

Under­stand­ing Brain Imag­ing

— By Chris Dud­ley, Matt Gasperetti, Mikey Nar­vaez, and Sarah Walors­ki

Do you remem­ber the anti-drug pub­lic ser­vice announce­ment from the 1980s that showed an egg fry­ing in a hot pan which rep­re­sent­ed your brain on drugs?

Dur­ing the 1990s, brain imag­ing moved beyond fried eggs as com­put­er tech­nol­o­gy allowed researchers to process large amounts of data required for func­tion­al imag­ing approach­es. As a result, the PSA men­tioned above no longer pro­vides the most accu­rate anal­o­gy illus­trat­ing what hap­pens to the brain when exposed to drugs.

Today, brain imag­ing research has helped cre­ate a sophis­ti­cat­ed “dis­ease mod­el of chem­i­cal depen­dence relat­ed to changes in the func­tion of neu­ro­trans­mit­ters and recep­tors in the brain. These cir­cuits are respon­si­ble for reward pro­cess­ing, mem­o­ry and learn­ing, moti­va­tion and dri­ve, in addi­tion to con­trol (Nora Volkow describes these cir­cuits in a 2004 lit­er­a­ture review).

This par­tic­u­lar post focus­es on the tech­niques used most com­mon­ly to study the brain’s role in addic­tion and oth­er men­tal health prob­lems. We will cov­er the prin­ci­ple behind each method, advan­tages and lim­i­ta­tions of each, and pro­vide an exam­ple of the results that can be obtained.

Beyond the Fry­ing Pan: EEG and CT

Elec­troen­cephalog­ra­phy (EEG) and Com­put­ed tomog­ra­phy (CT) were two of the first meth­ods used to study the brain. EEG uti­lizes elec­trodes placed on the scalp that mea­sure elec­tri­cal impuls­es, where­as CT cre­ates a three-dimen­sion­al image of the brain with two-dimen­sion­al x-rays.

EEG is a non-inva­sive pro­ce­dure with high tem­po­ral res­o­lu­tion; it is often used to record the brain’s response to a stim­u­lus (e.g. an indi­vid­ual ingests a drug and the change in brain activ­i­ty is record­ed).

EEG is lim­it­ed because it can only record data from the sur­face of the brain. In addi­tion, EEG does not pro­duce images of the brain it only mea­sures elec­tri­cal impuls­es.

CT is used to cre­ate three-dimen­sion­al images. Unfor­tu­nate­ly, CT can­not pro­duce high-res­o­lu­tion images of soft tis­sue (i.e. the brain) and requires high lev­els of radi­a­tion. While CT is still used, pre­dom­i­nate­ly to cre­ate images of the body, it has to be used infre­quent­ly to avoid exces­sive radi­a­tion expo­sure. Although EEG and CT did not teach us much about addic­tion, these meth­ods were the tech­no­log­i­cal pre­cur­sors to more egg-cel­lent brain imag­ing meth­ods.

Unscram­bling the Mys­ter­ies of the Brain with MRI and fMRI

Ever won­der what it’s like to have radio waves sent through your brain? Well, Mag­net­ic Res­o­nance Imag­ing (MRI) may be for you! MRI pro­duces high qual­i­ty images of the brain by using a large, cylin­dri­cal mag­net to cre­ate a mag­net­ic field around the head. Radio waves are sent through this field and alter hydro­gen nuclei in the brain. These detectable changes are sub­se­quent­ly trans­mit­ted to a com­put­er and used to gen­er­ate a series of images.

Using these images, sci­en­tists are able to deter­mine minute changes in the brain that occur over time by com­par­ing dif­fer­ent MRI scans.

MRI is use­ful because it can pro­duce high­er res­o­lu­tion images than CT scans and does not expose patients to exces­sive radi­a­tion. On the con­trary, MRI is lim­it­ed because there is no way to pro­duce high-res­o­lu­tion images mea­sur­ing tem­po­ral change.

This leads to the recent devel­op­ment of Func­tion­al Mag­net­ic Res­o­nance Imag­ing (fMRI). This tech­nique, devel­oped only recent­ly, has allowed sci­en­tist to use MRI tech­nol­o­gy to cap­ture images of var­i­ous brain func­tions.

Func­tion­al MRI focus­es on the flow of oxy­genat­ed blood with­in the brain. To sim­pli­fy things, when an area of the brain is stim­u­lat­ed, oxy­genat­ed blood rush­es to that area. Func­tion­al MRI is able to cap­ture this flow of blood because of the slight dif­fer­ence in mag­net­ism between oxy­genat­ed and deoxy­genat­ed blood.

This method is advan­ta­geous because it allows researchers to cap­ture a series of images every sec­ond. These images can be used to cre­ate “movies” mon­i­tor­ing changes in brain activ­i­ty.

By pro­duc­ing sequen­tial images, fMRI records the areas of the brain that are acti­vat­ed. In addi­tion to detect­ing sub­stance use, fMRI is also a good lie-detect­ing device, as it sens­es activ­i­ty in cer­tain regions of the brain asso­ci­at­ed with spe­cif­ic behav­iors.

Like all good things, includ­ing eggs, which con­tain a great deal of cho­les­terol, there is a down­side to fMRI: blood flow is only an indi­rect mea­sure of neu­ronal activ­i­ty and fMRI only shows where activ­i­ty takes place not exact­ly what is going on.

PET: Great Acronym, Great Images

Positron Emis­sion Tomog­ra­phy (PET) is anoth­er com­mon­ly used brain imag­ing tech­nique. PET, which is derived from CT, was the first func­tion­al imag­ing tech­nique.

This method uti­lizes small amounts of radio­trac­ers (i.e. mol­e­cules with a short-lived radioac­tive con­stituent atom such as car­bon-11 or oxy­gen-15), which are local­ized by sen­sors that cre­ate com­put­er-com­piled images. These images depict the rel­a­tive amount of radio­trac­er present by using a col­or gra­di­ent red being the high­est con­cen­tra­tion and blue the low­est.

Like fMRI, PET can be used to study region­al cere­bral blood flow (rCBF) via radio-labeled water in the blood­stream. Addi­tion­al­ly, PET can look at glu­cose metab­o­lism that shows region­al neu­ronal acti­va­tion.

Unfor­tu­nate­ly, PET can­not achieve the tem­po­ral or spa­tial res­o­lu­tion pos­si­ble with fMRI, and uses trace amounts of radi­a­tion: only one PET scan is allowed per year due to con­cerns regard­ing radi­a­tion expo­sure.

PET is most use­ful when study­ing neu­ro­trans­mit­ter func­tion and holds an advan­tage in tem­po­ral and spa­tial res­o­lu­tion over SPECT (dis­cussed below).

By using a radio-labeled neu­ro­trans­mit­ter, it is pos­si­ble to study the loca­tion a neurotransmitter’s action, the amount of neu­ro­trans­mit­ter release, and abun­dance of recep­tor lev­els. This has rel­e­vance in addic­tion stud­ies, which have shown that dopamine recep­tor lev­els decrease with long-term cocaine use, lead­ing to tol­er­ance to low drug dos­es.

The only down­side is that it takes time to devel­op appro­pri­ate radio­trac­ers. Cur­rent­ly, the dopamine, GABA, and cannabi­noid cir­cuits can be exam­ined, but suit­able radio­trac­ers for oth­er neu­ro­trans­mit­ters are still lack­ing. It is like­ly that future research will solve this prob­lem.

Egg SPECT to Be Amazed

The name Sin­gle Pho­ton Emis­sion Com­put­er­ized Tomog­ra­phy (SPECT) sounds impres­sive because it is. This method uti­lizes trac­ers that are direct­ly inject­ed into the body’s blood flow to high­light the lev­el of neu­ronal activ­i­ty in the brain.

After trac­ers are inject­ed, a “gam­ma” cam­era rotates around the head to record data, and a com­put­er uses the data to con­struct 2D or 3D images of active brain regions inac­tive areas of the brain show up as dark voids.

SPECT con­firms areas of the brain that cor­re­spond with a person’s neur­al activ­i­ty, and can be used to iden­ti­fy symp­toms asso­ci­at­ed with drug use or men­tal ill­ness. It can track the effects of coun­sel­ing and med­ica­tions: as an indi­vid­ual gets bet­ter, brain areas will change in activ­i­ty lev­el.

Although SPECT can’t cre­ate images as detailed as a PET scan, images can be viewed in both 2D and 3D. This method is not very expen­sive, and the pro­ce­dure doesn’t need as many tech­ni­cal and med­ical staff to com­plete. The fol­low­ing SPECT images illus­trate the effect of drug use on brain func­tion.

SPECT not only shows dam­age, but also shows improve­ment when sub­stance use is dis­con­tin­ued.

To see more exam­ples of how the brain is affect­ed by drug and alco­hol use using SPECT, click here: http://www.amenclinics.com/bp/atlas/ch15.php

Beyond Brain Imag­ing

We have come a long way since the fry­ing pan days. Clear­ly, the results of brain imag­ing stud­ies are very use­ful in that they help researchers bet­ter under­stand what hap­pens to a brain that has been fried by drugs.

Addi­tion­al­ly, poten­tial drug ther­a­py treat­ments have been sug­gest­ed based on the “cir­cuits” mod­el. The gen­er­al aim of this approach includes decreas­ing a drug’s reward val­ue, dis­so­ci­at­ing drug use from plea­sur­able mem­o­ries, and restor­ing nor­mal brain activ­i­ty.

While brain imag­ing is a very use­ful tool, it does not pro­vide a com­plete under­stand­ing of addic­tion. Each tech­nique has lim­i­ta­tions, as described above, but future devel­op­ments are sure to strength­en these tech­nolo­gies. In addi­tion, treat­ing addic­tion pure­ly as a brain dis­ease has its own lim­i­ta­tions, in that it ignores the pow­er­ful socio-cul­tur­al fac­tors that con­tribute to drug use.

And just like any­thing else with­in the sci­en­tif­ic realm, it is cru­cial that all hypothe­ses be rig­or­ous­ly test­ed: qual­i­ty of research meth­ods, and restraint when inter­pret­ing results, must not be sac­ri­ficed in order to draw excit­ing con­clu­sions.

Final­ly, it is impor­tant to note that brain imag­ing is only able to show cor­re­la­tions in data, not cau­sa­tions: as a wise pro­fes­sor once said, “lines drawn on a map can­not show you why coun­tries wage war.”  How­ev­er, in the future, increased sci­en­tif­ic under­stand­ing of brain addic­tion, as well as the results of future imag­ing stud­ies, may be able to show how bor­ders change as a result of war.

—-

Remem­ber, this blog post was writ­ten as part of a Neu­roan­thro­pol­o­gy class. You can find the oth­er sev­en blog posts by click­ing on Why A Final Essay When We Can Do This?. Enjoy!

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5 Responses

  1. Kerri says:

    I have suf­fered with a mood dis­or­der (Major Depres­sion) for over 10 years. I know SPECT imag­ing is used now in treat­ment sit­u­a­tions, do you have any infor­ma­tion regard­ing this research or how it can be used by the con­sumer? -Thanks, Ker­ri

  2. Jacob says:

    I met Dr. Amen at a lec­ture he gave and then par­tic­i­pat­ed in his brain study of injured and unin­jured brains. I learned a lot about the dam­age that can occur even from nor­mal children’s bangs to the head — the kind that hap­pen to most kids who engage in sports.

    If you are inter­est­ed in the brain and how it works, I high­ly rec­om­mend read­ing ““My Stroke of Insight”” by Dr. Jill Bolte Tay­lor. It’s on the NY Times Best­seller list and it’s a won­der­ful book. Dr. Taylor’s talk at TED dot com is also AMAZING! Oprah inter­viewed Dr. Tay­lor and you can check that out on Oprah.com. And Time Mag­a­zine named Dr. T one of the 100 Most Influ­en­tial peo­ple in the world. Hav­ing read her book, I can see why all the atten­tion.

    Dr. Amen’s book is brain sci­ence and it’s great at that. Dr. Tay­lor is a Har­vard Brain Sci­en­tist, but what she writes about is the sci­ence and much more. She real­ly cracks the code to under­stand how our brains (right and left hemi­spheres) work and she explains how we can get into our right brain and be hap­pi­er and more joy­ful. Aside from any of the sci­ence, My Stroke of Insight is also just a great sto­ry.

  3. Alvaro says:

    Dear Ker­ri, brain imag­ing such as SPECT may be use­ful for pro­fes­sion­als, but is not the main tool for either diag­no­sis or treat­ment. So it can be mis­lead­ing for con­sumers to expect too much from it. I encour­age you to con­sult with your doc­tor: he or she is the most qual­i­fied per­son to help you.

    Jacob: many thanks for your note. I heve in fact already ordered My Stroke of Insight for sum­mer read­ing!

  4. Nancy says:

    I met Dr. Amen too — in San Diego at a meet­ing by one of the Secret authors. He con­vinced me to try to get my son who plays soc­cer to wear the head­gear.
    I also heard Dr. Jill Bolte Taylor’s TED Talk video- http://www.ted.com/talks/jilltaylorwhen it was sent to me, and I read her book MY STROKE OF INSIGHT, which was one of the most pow­er­ful­ly mov­ing and inspir­ing books I’ve read in ages. The PhD brain scientist’s inside view of her own stroke was fas­ci­nat­ing. The spir­i­tu­al lessons and right/left brain lessons were pro­found.
    THank you for shar­ing that Jacob!

  5. Jayman says:

    Very good arti­cle. Good dis­ec­tion of the dif­fer­ent options avail­able for patients seek­ing fur­ther diag­no­sis and insight.

    I actu­al­ly use the PET and SPECT images shown here dur­ing lec­tures at my addic­tions clin­ic.

    I wel­come sug­ges­tions on where to find new research on addic­tion and brain dis­ease.

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As seen in The New York Times, The Wall Street Journal, BBC News, CNN, Reuters and more, SharpBrains is an independent market research firm tracking health and performance applications of brain science.

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