A Curious Consensus: Brain Scans Prove Disease?

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[sSRI-Research] A Curious Consensus: " Brain Scans Prove

Disease " ? - By Grace E. Jackson, MD

 

 

 

 

A Curious Consensus: " Brain Scans Prove Disease " ?

 

By Grace E. Jackson, MD

July 10, 2005

Introduction

 

 

 

1

Recently, a series of physicians have appeared on national news

programs, reassuring the public that psychiatric disorders have been

confirmed as " real " diseases of the brain.

 

Perhaps the context of these announcements -a heated exchange between

two Hollywood celebrities who have clashed over the medicalization and

treatment of postpartum depression -has prevented the media from

noticing serious inaccuracies in the recorded testimony of their

selected discussants:

 

" When you don't have enough neurotransmitters firing, making the

connections, your brain doesn't act like it should. And you can see

what a normal brain should look like. That is an objective measure. " 1

 

Dr. Sanjay Gupta

neurosurgeon / CNN Sr. medical correspondent

 

" .we can see differences between brain images of someone who is

depressed and someone who is not depressed. And if we give

medications, the brain of the depressed person goes back to looking

like a person not depressed. " 2

 

Dr. Nada Stotland

psychiatrist / Secretary, American Psychiatric Association

As none of the featured authorities has clarified the essential

distinction between anatomic and functional studies of the human

brain, a corrective analysis is necessary and overdue.

 

 

 

2

 

The Difference Between Anatomic and Physiological Studies of the Brain

 

Anatomic studies depend upon technologies such as computed tomography

(CT) and magnetic resonance imaging (MRI) to capture static images of

the brain. Because these techniques have been well replicated and

validated, they are routinely used by physicians to identify somatic

abnormalities, such as tumors, abscesses, or vascular malformations.

Despite attempts to the contrary, however, more than fifty years of

research have failed to confirm radiographic evidence linking any

psychiatric condition to a structural defect within the brain.3-5

 

Functional studies, on the other hand, depend upon technologies such

as functional MRI (fMRI) and positron emission tomography (PET). These

methodologies employ strong magnetic fields or radioactive isotopes,

respectively, for the purpose of evaluating brain processes when a

person is at rest or engaged in specific activity. Intra- and

interindividual investigations of this kind seek to identify the

underlying substrates of the nervous system which are presumed to be

uniquely involved in certain mental and psychological phenomena (e.g.,

during the processes of remembering, learning, perceiving, emoting,

intending).

 

Referring to the images on a functional brain scan in the course of a

recent news broadcast, Dr. Sanjay Gupta repeatedly avowed that the new

technologies display a visual record of brain activity:

 

" An ADHD brain is on the left side there. You can see, it's mainly on

the right side of the brain that things are activating. They should be

activating all over and on the left side as well. You see a non-ADHD

brain, again, it's different than the ADHD brain. These are

measurements that people take. This is the science that people have

been talking about and this is what a lot of treatment is predicated

on [sic]. " 6

 

However well intended, Dr. Gupta's remarks were nevertheless

misleading. First, there was no mention of the fact that fMRI, PET,

and other functional imaging modalities (such as magnetic resonance

spectroscopy and single photon emission computed tomography) are

incapable of measuring brain activity. Rather, what these technologies

actually reflect are transient changes in blood flow. Second, there

was no reference to the numerous confounds which undermine the

validity of most (if not all) comparison studies, as researchers

commonly fail to control for the influence of age, gender, body size

(weight and height), drugs (licit or illicit), medical conditions,

physical activity, education, and diet. Third, there was no

acknowledgement of the fact that the use of these technologies remains

controversial. Due to theoretical and practical limitations, their

application is restricted to research settings at this time. Why this

is true is the untold story which the news media and its chosen

experts have ignored.

 

 

3

 

The Limitations of Functional Imaging Technologies 7-11

 

The theory of neurovascular coupling

 

The clinical utility of functional neuroimaging depends upon the

premise that changes in regional blood flow correspond directly to

neural activity. This theory of neurovascular coupling suggests that

cellular activity (primarily within neurons) creates changes in the

consumption of oxygen and sugar. These cellular processes are believed

to recruit a regenerative surge in blood flow. Interestingly,

refutations of this theory have been provided by animal research

documenting shifts in regional blood flow in the absence of oxidative

metabolism or glycolysis. Similarly, the presence of cerebral hypoxia

and/or hypoglycemia in survivors of stroke or traumatic brain injury

has not been reliably associated with surges in blood flow. As

perplexing as these contradictions may seem, one can easily imagine

the existence of an alternative scenario, in which the homeostatic

mechanisms of the brain might shift blood into areas of underactivity

in an effort to revive cells which are sluggish or dormant. Until

neurophysiologists understand the cause and timing of changes in

cerebral blood flow, the implications of functional

imaging technologies will remain ambiguous.

 

The time lag associated with blood flow

 

Electrical brain events happen in a span of hundreds of milliseconds.

In contrast, the movement of fresh blood into an active tissue is

delayed by 1 to 3 seconds. This time lag limits the temporal

resolution of functional imaging technologies, because the scanner and

the brain are never in temporal synchrony (in the language of still

photography: the brain activity is like a flash of lightning for which

the scanner lacks an appropriate shutter speed). This results in the

unfortunate reality that functional imaging technologies may be able

to provide information about certain locations associated with mental

phenomena, but not about the onset or duration of the inciting events.

 

The localization of neuronal activity

 

Since vascular and electrical processes cannot be co-determined inside

the brains of humans, researchers have experimented upon a variety of

non-human species. A significant body of work has revealed the fact

that sections of the neocortex can experience changes in blood flow

and metabolism without firing an action potential of their own (no

spiking). These findings have tremendous scientific import, for they

suggest that the intensities which appear on functional brain scans

might not reflect the electrical activity of the underlying regions.

Rather, the bright spots might reflect the activity of remote

(invisible) cell populations whose action potentials have propagated a

certain distance but not moved on (inhibitory post-synaptic potentials

> excitatory post-synaptic potentials).

4

 

The statistical averaging of images

 

Because the contrast resolution of the functional neuroimaging

technologies is so poor (the " activated vs. baseline " differences which

they capture are extraordinarily small - on the order of a mere 2-5%),

multiple scans must be obtained for the purpose of achieving

statistical significance (i.e., to rule out the possibility that the

observed changes have occurred simply by chance). Consequently, when

reports about " between group " differences are based upon functional

technologies, it means that the brain scans of several individuals

have been integrated by computer software in order to produce a

composite or average result.

 

When physicians like Dr. Gupta display the picture of an ADHD brain,

they are not referring to any specific child or adult. Rather, they

refer to an image which reflects a subset of the population whose

brain features have been averaged together. The final graphic may or

may not resemble any real person. High rates of intra- and

interindividual variability reduce the sensitivity and specificity of

these procedures, so that they cannot be used dependably in the

clinical setting.

 

The subtraction method of analysis (paired image subtraction)

 

 

The subtraction method of analysis infers neural activity by

subtracting baseline from activated scans, or by subtracting the

images of controls from " abnormals. " For example, if an experimental

task activates zones 1, 2, and 3 in a healthy subject, and zones 1, 2,

3, and 4 in the brain of a patient, zone 4 would be interpreted as the

substrate responsible for aberrant behavior. The problem with this

approach lies in the assumption that the difference between two tasks

(active vs. resting) or two conditions (healthy vs. ill) can be

divided into separable and mutually exclusive cortical or subcortical

components, and that changes in regional blood flow will correspond

neatly to these specialized units of the brain.

 

 

 

The premature assumptions of safety

 

Functional neuroimaging technologies pose dangers which remain largely

unexplored. The magnetic fields used in MRI have been found to disrupt

the blood brain barrier in several animal studies. If similar

perturbations occur in humans, it is possible that even transient

changes arising from the exposure to these increasingly powerful

devices (up to 7 Tesla) might permit toxins and other plasma

components to enter the brain parenchyma, where they could initiate

inflammatory or autoimmune responses. Furthermore, the long term

health effects of ionizing radiation (i.e., the gamma rays produced by

the annihilation photons of PET) are equally unclear. It is important

to appreciate the fact that the potential mutagenicity of

radioisotopes is greater when a given dose is administered over

minutes to hours (as occurs in psychiatric research protocols) as

compared to gradual exposures over months to years. No dose of

ionizing radiation is hazard free,12-13 and the potential risks (of

cancers, birth defects, heart disease) are cumulative, not fleeting.

5

 

Conclusion

 

It is notable that the official website of the American Psychiatric

Association features a

position paper (January 2005) regarding the use of functional imaging

technologies in

children and teens:

 

" Imaging research cannot yet be used to diagnose psychiatric illness

and may not be useful in clinical practice for a number of

years.Specifically, no published investigation in the field has

determined that any structural or functional abnormality is specific

to a single psychiatric disorder.

 

 

Additionally, imaging studies examine groups of patients and groups of

healthy controls; therefore, findings may not apply to all individuals

with a given disorder. Even when significant differences are

identified between groups, there is a substantial overlap among

individuals in both groups. " We conclude that, at the present time, the

available evidence does not support the use of brain imaging for

clinical diagnosis or treatment of psychiatric disorders. " 14

 

Contrary to the reports which have been emphasized by the major news

outlets, there is

no evidence to justify the claim that psychiatric disorders arise from

anatomic or physiological abnormalities in the brain. Based upon a

variety of theoretical and practical limitations, the functional

imaging technologies cannot identify the origin of mental phenomena.

Philosophical observers might suggest a host of reasons

(epistemological and ontological) why they never will.

 

The media have the power to shape popular and professional perceptions

by disseminating the facts of science, or by perpetuating science

fictions. Responsible journalism accepts the challenge of embracing

the former, while avoiding the latter.

 

 

===============================================================

Notes

1 " Scientologist Explains Tom Cruise's Recent Anti-Psychiatry

comments, " Anderson

Cooper 360 Degrees. CNN, New York. 30 JUN 2005. Transcript.

2 Ibid.

3 Darin D. Dougherty, Scott L. Rauch, and Jerrold F. Rosenbaum, Ed.,

Essentials of

Neuroimaging for Clinical Practice, (Washington, DC: American

Psychiatric Publishing,

Inc., 2004), pp. 13-14, 49-51.

6

4 U.S. Department of Health and Human Services, Mental Health: A

Report of the

Surgeon General, (Rockville, MD: U.S. Department of Health and Human

Services,

1999), p. 15.

5 Robert E. Hales, Stuart C. Yudofsky, and John A. Talbott, Ed., The

American

Psychiatric Press Textbook of Psychiatry, 3rd Edition, (Washington,

DC: American

Psychiatric Press, Inc., 1999), pp. 300-304.

6 " Scientologist Explains Tom Cruise's Recent Anti-Psychiatry

comments, " Anderson

Cooper 360 Degrees. CNN, New York. 30 JUN 2005. Transcript.

7 Cheryl J. Aine, " A Conceptual Overview and Critique of Functional

Neuroimaging

Techniques in Humans: I. MRI/fMRI and PET, " Critical Reviews in

Neurobiology

9 (1995), pp. 229-209.

8 David J. Heeger and David Ress, " What Does fMRI Telll Us About Neuronal

Activity? " Nature Reviews 3 (2002): 142-151.

9 Russell A. Poldrack, " Imaging Brain Plasticity: Conceptual and

Methodological Issues

- A Theoretical Review, " NeuroImage 12 (2000): 1-13.

10 Dara S. Manoach, Elkan F. Halpern, Todd S. Kramer, Yuchiao Chang,

Donald C.

Goff, et. al., " Test-Retest Reliability of a Functional MRIWorking

Memory Paradigm in

Normal and Schizophrenic Subjects, " American Journal of Psychiatry 158

(2001):

955-958.

11 G.D. Honey, P.C. Fletcher, and E.T. Bullmore, " Functional brain

mapping of psychopathology, " Journal of Neurology, Neurosurgery, and

Psychiatry 72 (2002): 432-439.

12 John W. Gofman, Preventing Breast Cancer: The Story of a Major,

Proven, Preventable Cause of This Disease, 2nd Ed., (San Francisco:

C.N.R. Book Division,

1996).

13 John W. Gofman, Radiation from Medical Procedures in the

Pathogenesis of Cancer and Ischemic Heart Disease: Dose-Response

Studies with Physicians per 100,000 Population, (San Francisco: C.N.R.

Book Division, 1999).

14 Loris Talbott Flaherty, William Arroyo, Irene Chatoor, Roxanne

Dryden Edwards, Yvonne B. Ferguson, et. al., " Brain Imaging and Child

and Adolescent Psychiatry With Special Emphasis on SPECT, " (January

2005), retrieved on 09 JUL 05 at:

<www.psych.org/psych_pract/clin_issues/ populations/children/SPECT.pdf>.