Clinical review

Functional magnetic resonance imaging in neuropsychiatry

Catherine Longworth, research worker,  Garry Honey, research worker,  Tonmoy Sharma, senior lecturer. 

Section of Cognitive Psychopharmacology, Department of Psychological Medicine, Institute of Psychiatry, London SE5 8AF

Correspondence to: T Sharma t.sharma{at}iop.kcl.ac.uk

The ability of functional magnetic resonance imaging to provide high quality imaging of brain function without the need for radioactive tracers is rapidly making it the technique of choice for research into neuropsychiatric disorders and their treatment. The future is likely to bring a closer involvement in clinical practice, with the technique being used for early detection of dysfunction, assessing the clinical efficacy of drug treatments, and as an alternative to invasive preoperative procedures requiring localisation of function.

	Functional magnetic resonance imaging

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The development of anatomical neuroimaging enabled the in vivo visualisation of neuropathology in conditions such as stroke, facilitating differential diagnoses and early treatment. Since then scanning techniques have gone beyond structural detail to provide images relating to human brain function, and in the past decade these techniques have been joined by an impressive new imaging tool, functional magnetic resonance imaging (functional MRI). This has a spatial resolution within the millimetre scale and can capture responses in the brain occurring over a few seconds, although reconstruction and processing of the raw data commonly occur after scanning. Functional MRI is non-invasive and safe. It does not require radioactive tracer substances, unlike positron emission tomography (PET) or single photon emission tomography (SPET), and uses the brain's natural haemodynamic response to neural activity as an endogenous tracer. It can be carried out during the same session as routine magnetic resonance imaging in a clinical scanner. These features are making it increasingly popular in neuropsychiatric research.

The commonest form of functional MRI is blood oxygenation level dependent (BOLD) imaging.¹ The BOLD signal depends on the ratio of oxygenated to deoxygenated haemoglobin. In regions of neuronal activity this ratio changes as increased flow of oxygenated blood temporarily surpasses consumption, decreasing the level of paramagnetic deoxyhaemoglobin. These localised changes cause increases in magnetic resonance signal, which are used as markers of functional activation (fig 1). Ultrafast scanning can measure these changes in signal, which are mapped directly onto a high resolution scan of the subject's anatomy. In addition, data from several subjects can be combined to provide group averaged images mapped into standard neurological coordinates.

View larger version (47K): [in this window] [in a new window]   Fig 1.    Principles involved in converting neuronal activity into a blood oxygenation level dependent (BOLD) signal, which can be measured with functional magnetic resonance imaging

Most functional MRI involves measuring the BOLD signal while people are engaged in carefully controlled tasks. During a scan subjects lie within the bore of the magnet, and their behavioural responses to presented stimuli are monitored. A wide range of stimuli can be presented across sensory modalities. It is possible to examine covert phenomena such as thinking, planning, or hallucinating as well as overt motor responses, such as generating a specific movement or signalling the answer to a question by pressing a button. Sophisticated methods of data analysis are used to test whether changes in signal during performance of a task are statistically reliable.²

In several direct comparisons functional MRI has been able to replicate findings from positron emission tomography,³ suggesting that the non-invasive functional MRI should be used whenever possible to avoid exposure to radiation and the need for an expensive cyclotron unit on site. Unlike positron emission tomography, functional MRI is not limited in the number of scans that can safely be performed on a single person, which means that repeated scans of the same patient can track the course of a disorder and, potentially, its response to treatment. The safety of the technique also facilitates the recruitment of research subjects and enhances compliance, as well as extending the range of people who can be scanned to vulnerable groups such as children.

Like all neuroimaging methods, functional MRI has limitations. Movement of subjects during scanning can produce artefacts, although these can be resolved to a certain extent by corrective data procedures.⁴ The magnetic resonance properties of the anterior skull base and petrous bone are another source of artefacts, causing a relative loss of signal in the medial inferior frontal lobe and inferior temporal lobe.⁵ This problem can be reduced through careful choice of orientation of the scan, but it must be considered when interpreting results. There are also issues of a practical nature, such as the careful screening necessary to ensure that candidates for a scan can tolerate the noise of the scanner and close confinement within the magnet bore, as well as being free of metallic implants.

	Applications to neuropsychiatric disorders

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The infrastructure necessary for conducting functional MRI is already available in the magnetic resonance imaging departments of district general hospitals. It can be carried out on standard clinical MRI scanners with upgraded software. However, as with any new technology, established findings and standardised techniques will be required before functional MRI can make the transition from research to routine use in clinical practice. Its main applications to neuropsychiatry at present are to increase understanding of a wide range of disease states and the effects of treatment.

Functional MRI can provide a window into disease states, such as depression or schizophrenia, that, because of the lack of biological markers, are currently diagnosed on the basis of behavioural signs and self reported symptoms such as auditory hallucinations. Functional MRI has the potential to change our understanding of these conditions by demonstrating how neural dysfunction manifests itself in behaviour and symptoms.

Unipolar depression
One study compared depressed patients and healthy volunteers in their neural response to film clips designed to evoke transient sadness.⁶ The brain activation recorded during emotionally neutral film clips was compared with that occurring during sad films. This revealed that, although many brain regions were activated similarly by both groups, the depressed subjects activated additional regions, namely the left medial prefrontal cortex and the right anterior cingulate gyrus, during the processing of transient sadness. These brain structures are thought to be involved in the attribution of emotional importance and the conscious experience of emotion. The investigators postulated that in depression abnormal frontal activity might disconnect the limbic system from normal modulatory influences.

Schizophrenia
Patients with schizophrenia show specific deficits in language processing, which are classically considered a cardinal feature of the illness. Functional MRI has begun to reveal the neural dysfunction underlying these deficits.⁷ We found that patients performing a language task showed a broadly similar pattern of neural activation, though with an attenuated power of response, compared with controls.⁸ However, we observed specific regions of hypoactivity in the frontotemporal cortex (fig 2). These may be related to deficits in language processing that can be observed at a cognitive level.

View larger version (37K): [in this window] [in a new window]   Fig 2.    Functional MRI images showing reduced activation of language areas during a linguistic task in patients with schizophrenia (from Honey et al8)

View larger version (33K): [in this window] [in a new window]   Fig 3.    Functional MRI images showing abnormal cerebral asymmetry during a psychomotor task performed by people with schizophrenia (Honey et al11)

Alzheimer's disease
In disorders where neural correlates have been identified, such as Alzheimer's disease and epilepsy, research has focused on establishing that functional MRI can adequately replicate existing clinical findings from more invasive techniques. For example, Sandson et al used a variant of functional MRI to investigate cerebral hypoperfusion in patients with Alzheimer's disease.¹⁶ They replicated previously demonstrated temperoparietal hypoperfusion and found it to correlate with the severity of the dementia. Indeed, Harris et al reported that, with a non-radioactive magnetic contrast agent, functional MRI could detect such hypoperfusion at an early stage in the disorder when symptoms were still mild.¹⁷ Together, these studies indicate that functional MRI shows promise as a clinical tool for the early detection of Alzheimer's disease.

Epilepsy
Another potential use of functional MRI is in the presurgical testing of patients with intractable epilepsy. In cases where temporal lobe resection is considered patients undergo lateralisation testing of temporal lobe functions to establish the risk of permanent neurological damage. This is commonly achieved by testing language and memory abilities after an injection of sodium amylobarbitone into an internal carotid artery to anaesthetise one hemisphere or by direct electrical stimulation. Research has shown that functional MRI can replicate the results of these tests, raising the possibility of replacing distressing and potentially harmful procedures.¹⁸ In the United States, functional MRI of sensorimotor and language functions has been used to assess whether a patient is a candidate for surgery and to guide surgical planning in cases of vascular malformations, tumours, intractable epilepsy, and lesions near critical cortical areas.¹⁹

	Clinical implications of technological advances

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Functional MRI is still in its infancy. This decade we have seen many technical developments, and we can expect to see further improvements. Currently, functional MRI is mainly used in neuropsychiatry to investigate static aspects of disorders. Improving the temporal resolution of scanning extends the range of disease processes that can be investigated to include even momentary phenomena such as individual psychotic hallucinations. Researchers have begun to achieve this by combining functional MRI with electrophysiological techniques such as electroencephalography and magnetoencephalography.²⁰

Another new development, real time functional MRI, displays the course of neurological activation during the scan rather than processing the data after scanning. This is particularly useful for clinical practice as it allows immediate assessment of brain activation and movement within the scanner, thus adding to the potential of functional MRI as a useful presurgical tool.²¹ It might also be possible to use real time scanning in treatments based on biofeedbackthat is, the self modulation of physiological parameters in response to simultaneous feedback of biological information. For example, in cases of intractable epilepsy it has been found that training patients to alter the pattern of their electroencephalogram reduced seizure rates over a six month period.²² With real time functional MRI, it might become possible to show patients images of their own brain function while they are in the scanner in order to facilitate biofeedback.

	Footnotes

   Competing interests: None declared.

	References

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1.	Ogawa S, Lee TM, Kay DW, Tank DW. Brain magnetic resonance imaging with contrast dependent on blood oxygenation. Proc Natl Acad Sci USA 1990; 87: 9868-9872[Abstract/Free Full Text].
2.	Bullmore ET, Williams SCR, Rabe-Hesketh S, Janot N, David A, Mellers J, et al. Statistical methods of estimation and inference for functional MR image analysis. Magn Reson Med 1996; 35: 261-277[Medline].
3.	Paulesu E, Connelly A, Frith CD, Friston KJ, Heather J, Myers R, et al. Functional MR imaging correlations with positron emission tomography. Initial experience using a cognitive activation paradigm on verbal working memory. Neuroimaging Clin North Am 1995; 5: 207-225.
4.	Bullmore ET, Brammer MJ, Rabe-Hesketh S, Curtis VA, Morris RE, Williams SCR, et al. Methods for diagnosis and treatment of stimulus correlated motion in generic brain activation studies using fMRI. Hum Brain Map 1999; 7: 38-48[Medline].
5.	Ojemann JG, Kbudak E, Snyder AZ, McKinstry RC, Racihle ME, Conturo TE. Anatomic localization and quantitative analysis of gradient refocused echo-planar fMRI susceptibility artifacts. Neuroimage 1997; 6: 156-167[Medline].
6.	Beauregard M, Leroux JM, Bergman S, Arzoumanian Y, Beaudoin G, Bourgouin P, et al. The functional neuroanatomy of major depression: an fMRI study using an emotional activation paradigm. Neuroreport 1998; 9: 3253-3258[Medline].
7.	Curtis VA, Bullmore ET, Brammer MJ, Wright IC, Williams SC, Morris RG, et al. Attenuated frontal activation during a verbal fluency task in patients with schizophrenia. Am J Psychiatry 1998; 155: 1056-1063[Abstract/Free Full Text].
8.	Honey GD, Soni W, Bullmore ET, Varatheeson M, Williams SCR, Andrew C, et al. Dissecting the components of linguistic processing in schizophrenia using functional MRI. Schizophr Res 1998; 29: 65.
9.	Wenz F, Schad LR, Knopp MV, Baudendistel KT, Flomer F, Schroder J, et al. Functional magnetic resonance imaging at 1.5 T: activation pattern in schizophrenic patients receiving neuroleptic medication. Magn Reson Imaging 1994; 12: 975-982[Medline].
10.	Mattay VS, Callicott JH, Bertolino A, Santha AK, Tallent KA, Goldberg TE, et al. Abnormal functional lateralization of the sensorimotor cortex in patients with schizophrenia. Neuroreport 1997; 8: 2977-2984[Medline].
11.	Honey GD, Soni W, Bullmore ET, Varatheesan M, Williams SCR, Andrew CM, et al. Evidence of abnormal lateralisation of motor systems in schizophrenia using functional MRI. Schizophr Res 1998; 29: 70.
12.	Howard R, David A, Woodruff P, Mellers I, Wright J, Brammer M, et al. Seeing visual hallucinations with functional magnetic resonance imaging. Dementia Geriatr Cogn Disord 1995; 8: 73-77.
13.	Woodruff PW, Wright IC, Bullmore ET, Brammer M, Howard RJ, Williams SC, et al. Auditory hallucinations and the temporal cortical response to speech in schizophrenia: a functional magnetic resonance imaging study. Am J Psychiatry 1997; 154: 1676-1682[Abstract/Free Full Text].
14.	Honey GD, Bullmore ET, Soni W, Varatheesan M, Williams SCR, Sharma T. Risperidone restores fronto-parietal activation by a working memory task in patients with schizophrenia [abstract]. Schizophr Res 1999; 36: 223.
15.	Honey GD, Bullmore ET, Soni W, Varatheesan M, Williams SCR, Sharma T. Investigation of the effect of typical versus atypical antipsychotics on motor function using functional MRI [abstract]. Schizophr Res 1999; 36: 223.
16.	Sandson TA, O'Connor M, Sperling RA, Edelman RR, Warach S. Noninvasive perfusion MRI in Alzheimer's disease: a preliminary report. Neurology 1996; 47: 1339-1342[Abstract/Free Full Text].
17.	Harris GJ, Lewis RF, Satlin A, English CD, Scott TM, Yurgelun-Todd DA, et al. Dynamic susceptibility contrast MRI of regional cerebral blood volume in Alzheimer's disease. Am J Psychiatry 1996; 153: 721-724[Abstract/Free Full Text].
18.	Bookheimer SY. Functional MRI applications in clinical epilepsy. Neuroimage 1996; 4(3 Pt 3): S139-S146[Medline].
19.	Buchbinder BR, Cosgrove GR. Cortical activation MR studies in brain disorders. Magn Reson Imaging Clin North Am 1998; 6: 67-93.
20.	George JS, Aine CJ, Mosher JC, Schmidt DM, Ranken DM, Schlitt HA, et al. Mapping function in the human brain with magnetoencephalography, anatomical magnetic resonance imaging, and functional magnetic resonance imaging. J Clin Neurophysiol 1995; 12: 406-431[Medline].
21.	Van Muiswinkle AMC, van den Brink JS, Folkers PJM. Real-time fMRI on a clinical MR scanner. Neuroimage 1999; 9(2): S212.
22.	Kotchoubey B, Blankenhorn V, Froscher W, Strehl U, Birbaumer N. Stability of cortical self-regulation in epilepsy patients. Neuroreport 1997; 8: 1867-1870[Medline].