Semiautomatic brain region extraction: a method of parcellating brain regions from structural magnetic resonance images.

Structural MR imaging has become essential to the evaluation of regional brain changes in both healthy aging and disease-related processes. Several methods have been developed to measure structure size and regional brain volumes, but many of these methods involve substantial manual tracing and/or landmark identification. We present a new technique, semiautomatic brain region extraction (SABRE), for the rapid and reliable parcellation of cortical and subcortical brain regions. We combine the SABRE parcellation with tissue compartment segmentation [NeuroImage 17 (2002) 1087] to produce measures of gray matter (GM), white matter (WM), ventricular CSF, and sulcal CSF for 26 brain regions. Because SABRE restricts user input to a few easily identified landmarks, inter-rater reliability is high for all volumes, with all coefficients between 0.91 and 0.99. To assess construct validity, we contrasted SABRE-derived volumetric data from healthy young and older adults. Results from the SABRE parcellation and tissue segmentation showed significant differences in multiple brain regions in keeping with regional atrophy described in the literature by researchers using lengthy manual tracing methods. Our findings show that SABRE is a reliable semiautomatic method for assessing regional tissue volumes that provides significant timesavings over purely manual methods, yet maintains information about individual cortical landmarks.

Working memory in another dimension: functional imaging of human olfactory working memory.

The majority of working memory research has been carried out within the visual and auditory modalities, leaving it unclear how other modalities would map onto currently proposed working memory models. In this study we examined the previously uninvestigated area of olfactory working memory. Our aim was to investigate if olfactory working memory would engage prefrontal regions known to be involved in working memory for other sensory modalities. Using positron emission tomography we measured cerebral blood flow changes in 12 volunteers during an olfactory working memory task and a comparison visual working memory task. Our findings indicate that both olfactory and face working memory engaged dorsolateral and ventrolateral frontal cortex when the task requirements were matched; a conjunction analysis indicated overlap in the distribution of activity in the two tasks. Similarities and differences in activity were noted in parietal lobe regions, with both tasks engaging inferior areas of 40/7, but only visual working memory showing increased activity within left superior parietal cortex. The findings support the idea that working memory processes engage frontal cortical areas independent of the modality of input, but do not rule out the possibility of modality-specific neural populations within dorsolateral or ventrolateral cortex.

Face learning and memory: the twins test.

The clinical utility of current face recognition tests has been questioned. To evaluate if a new paradigm may measure this type of memory more accurately, the authors created a novel test to examine face learning (previously uninvestigated) and short- and long-term retention. For this initial investigation of test sensitivity to hemisphere of dysfunction, patients with surgical resection from a temporal lobe and healthy subjects were tested. Recognition was evaluated on 3 trials: after a single exposure, after 4 exposures (for learning), and after a 24-hr delay interval. Patients with a right resection performed significantly worse than healthy controls and patients with left resection. There was no difference between patients with a left resection and controls. Classification of individual patients to side of resection based on test results showed higher sensitivity (82%) than published for other tests and maintained good specificity (79%).

Human brain function during odor encoding and recognition. A PET activation study.

In previous positron emission tomography (PET) studies we have shown significant regional cerebral blood flow (rCBF) increases during olfactory stimulation: unilaterally in the right orbitofrontal cortex, and bilaterally in the inferior frontal and temporal lobes (piriform cortex). In the present study we investigated brain function during different stages of olfactory memory processing. Subjects were scanned during four tasks: odor encoding, long-term odor recognition, short-term odor recognition and a no-odor sensorimotor control task. Subjects were 12 right-handed healthy volunteers (6 men, 6 women). Each subject underwent a training session four days prior to their PET scan to learn the six odors required for the long-term memory scan. PET scans were obtained with a Siemens Exact ECAT HR+ 3D system using H2(15)O methodology and 60-sec scanning intervals. PET images were coregistered with each subject's magnetic resonance imaging scan, averaged, and transformed into standard stereotaxic space. Paired image subtractions were analyzed for rCBF changes. Preliminary analyses have revealed significant activation of the right orbitofrontal region and bilateral piriform cortices during the long-term odor recognition task compared with the control task. Activation of the right piriform cortex was present during the short-term recognition task. Brain activity during encoding and retrieval tasks also involved prefrontal cortices. PET activation studies of memory in other modalities have led to hypotheses of a hemispheric encoding/retrieval asymmetry in frontal cortex; the generalizability of this theory to olfactory memory will be discussed.

Sodium amobarbital memory tests: what do they predict?

Severe transient postoperative memory deficits among epilepsy patients with resection from one temporal lobe may be indicative of increased risk for amnesia had more extensive removal of mesial structures occurred. Immediate postoperative testing may provide some validation for risk of amnesia as predicted by the intracarotid sodium amobarbital memory test (IAP-M). Thirty patients (24 not considered at risk for amnesia and 5 who failed the IAP-M) were tested on the first, second, and third days following resection from the right or left temporal lobe. Results suggest that the IAP-M paradigm used does not necessarily predict postoperative memory performance.