fMRI tests assumptions about behavior and thought

August 1, 2007

From illustrating the effects of minor head injury to showing the brain activation underlying childhood intelligence, studies that combine psychological tests and functional MRI are a powerful and versatile way to make connections between human behavior and neurophysiology.

From illustrating the effects of minor head injury to showing the brain activation underlying childhood intelligence, studies that combine psychological tests and functional MRI are a powerful and versatile way to make connections between human behavior and neurophysiology.

Such studies have become staples of the ISMRM annual meeting over the last five years. Investigators have extracted otherwise inaccessible information from brain activation studies to derive insight about depression, schizophrenia, deception and truth, memory, pain and its treatment, addiction, appetite, and other behaviors. New discoveries were added to the list of previous accomplishments this year.

Dr. Marion Smits used fMRI brain activation to investigate why some people experience lingering bouts of fatigue, headaches, and attention and memory deficits months after a minor head injury. Conventional MR brain studies have failed to find anatomical abnormalities that might explain moderate post-traumatic symptoms. Differences did appear, however, when Smits, a radiology resident at Erasmus Medical Center in Rotterdam, the Netherlands, compared the fMRI activation studies of 22 patients examined one month after mild head injury with those of 11 healthy volunteers.

With minor variations, the functional imaging and memory test protocols applied in Smits's study have become fairly standard for such investigations. The researchers generated activation maps to reveal the regional brain perfusion patterns captured with T2*-weighted gradient-echo/echo planar imaging. Three-D inversion recovery imaging produced anatomical references on which the color-coded functional data were overlaid.

The mental challenge involved a 30-second parametric block design that tested several levels of working memory load: 0-back (subjects were asked to push a button every time a zero was presented), 1-back (when a current number repeated a previous number), and 2-back (when a current number was the same as the second to last number).

Smits discovered areas of activation in the parahippocampal gyrus and a much larger area of activation in the posterior cingulate gyrus in the head-injury subjects than in the healthy controls. The findings suggest that minor head injury patients recruit new areas of the brain when performing difficult working memory load tests. These new areas are related to memory processing but have also been implicated in cognitive disorders such as mild cognitive deficit, a possible precursor to Alzheimer's disease, she said.

Dr. Irene Neuner, chair of psychiatry and psychotherapy at Rheinisch-Westfalische Technische Hochschule-Aachen University in Germany, adopted a similar format to discover clues to the neurophysiological origin of the vocal outbursts associated with Tourette's syndrome.

Her findings were drawn from blood oxygen level-dependent activation maps of 19 Tourette's patients, eight of whom were unmedicated, and 19 healthy volunteers. During imaging, the subjects were administered a parametric block design test that exposed them to happy, sad, angry, disgusted, and neutral-emotion faces. BOLD-effect activation in the amygdala, a region of the brain associated with emotional arousal, was relatively high for all the faces for Tourette's patients compared with the controls, but it was especially pronounced for angry, fearful, and neutral faces.

High amygdala activation could be expected as a response to angry and fearful faces, but the high activation for the neutral face was surprising, Neuner said. It suggested a possible association with the impulsive behaviors associated with the disease. The elevated amygdala activation may explain the vocal tics of Tourette's patients and why the patients cannot associate the outbursts with any specific external trigger, she said.

The amygdala also figured in an abstract presented by Zhihao Li, Ph.D., of Emory University. The presentation dealt with the long-term effects of prenatal exposure to cocaine. His examination of 12 teenagers with such a medical history and six age-matched volunteers found that the amygdalae of 17-year-olds who had been exposed to cocaine in utero were more responsive to emotional stimuli than control subjects. When challenged by negative emotional distractions embedded in the test, they recruited a more extensive brain network to support working memory functions than did the controls.

Using fMRI and a 30-second on-off block design test performed on 303 normal children, Vincent J. Schmithorst, Ph.D., a research instructor in pediatric brain imaging at Children's Hospital in Cincinnati, discovered differences in the way girls and boys process data in six regions of the brain related to IQ. Girls showed a greater reliance on connectivity between Wernicke's area and the posterior superior temporal gyrus, with a developmental effect seen in the right hemisphere. Boys showed more functional connectivity between Broca's area and the auditory processing regions of Wernicke's area and the right posterior superior temporal gyrus.

The findings are consistent with earlier studies showing sex-related differences in the posterior language areas for higher order semantic processing of sentences and more spatially distinct networks for phonetic and semantic processing in boys, Schmithorst said.