Four patients with conduction aphasia and impaired auditory but relatively preserved visual digit spans were tested in a task of short-term memory, a digit probe identification task, in both the visual and auditory modalities. Five age-matched normal subjects served as controls. Behavioural measures of response accuracy and reaction time and scalp derived event-related potentials were determined as a function of the number of items to be remembered. These measures were also recorded in a task requiring the detection of infrequent stimuli ('oddball' paradigm). The patients' performance and event-related potential wave forms for the 'oddball' task were no different from those of the controls. In the digit probe identification tasks the patients showed a reduction in amplitude of a positive component at a latency of approximately 450 ms (P450) of the event-related potential to correctly identified probes in the auditory modality. This component was within normal limits with visual testing. There was an inordinate increase in the patients' reaction time to auditory but not visual stimuli when the number of items to be remembered increased from one to three. Event-related potentials were also analysed as a function of speed of reaction time, position of the matching item in the stimulus presentation set and whether the probe was correctly identified as being in-set or out-of-set. Event-related potentials associated with fast reaction times in the auditory task when a single item was presented were no different between patients and controls, indicating that patients were capable of both performing normally and generating normal potentials on some trials. The data suggest that the deficit in auditory short-term memory in these patients occurs during stimulus classification.

Event-related potentials were measured in normal young subjects during a memory-scanning paradigm modified from one proposed by Sternberg. The stimuli used were verbal (digits) and non-verbal (musical notes) with the verbal stimuli and notes presented acoustically and the verbal stimuli also presented visually. In this paradigm each set of stimuli was presented for memorization, and then, after a 2 sec interval, a probe item appeared and was identified by the subject as belonging or not belonging to the memorized set. Memorized set sizes of 1, 3 and 5 items were studied. The potentials are described in terms of scalp distribution, latency and amplitude, and are compared with behavioral descriptors of performance (accuracy and reaction time). These potentials are also compared with those evoked by an auditory target-detection task ('odd-ball' paradigm) in the same subject at the same session. The potentials evoked by the probe stimuli consisted of a positive (P50-90), negative (N100-150), positive (P185-225) sequence in the first 250 msec, followed by a later, long-lasting (approximately 700 msec) positive component (labeled P3). This positivity consisted of an earlier component (latency of approximately 350-400 msec) with a frontal distribution, followed by a larger and later parietal component. The amplitude of the frontal component and the latency of the parietal component varied with the number of items in the memorized set differently from behavioral reaction times. Stimulus modality also affected both the amplitude and latency of the sustained parietal positive potential. Memory processes associated with the P3 complex in the 'odd-ball' task and the long-lasting positivity in the memory-scanning task are discussed.

These studies document a series of brain events accompanying short-term memory functions. For auditory verbal material the sequence involves at least two different sites within auditory cortex subserving sensory and cognitive processes of memorization. During the scanning of the short-term store structures within the medial temporal lobes, presumably the hippocampus, are active. There is an inconsistency between these results and the clinical observations of the need for an intact dominant parietal lobe for auditory short-term memory to function normally. Magnetic recordings showed no focal dipolar source of activity in the parietal lobe during any aspect of auditory short-term memory. The discrepancy could be accounted for by considering the parietal lobe lesion as "disconnecting" the lateral temporal cortex from the deep medial hippocampal structures thereby impeding auditory short-term functions (Geschwind, 1965). These studies show that the physiological analysis of brain events in the msec range can provide information about relatively complex cognitive processes underlying short-term memory. The magnetic and electrical recording methods provide a noninvasive way to study human brain functions involved in cognition that can then be correlated with behavioral measures of specific cognitive activities.

Background

The ability to measure the expression of proinflammatory cytokines from intestinal biopsies in patients with Crohn's disease in an accurate and reproducible way is critical for proof-of-concept and mechanism-of-action trials; however, the number of biopsies from a segment of the ileum or colon required to yield reproducible results has not been rigorously evaluated. We examined intestinal biopsies from patients with Crohn's disease to validate methods for detecting changes in inflammatory gene expression.

Methods

To evaluate the reproducibility of gene expression measurements, intestinal biopsies were obtained from designated segments from 6 healthy controls, 6 patients with active Crohn's disease, and 6 patients with inactive Crohn's disease. Disease activity was based on the simple endoscopic score for Crohn's disease. Expression of 7 proinflammatory genes was measured from each biopsy using quantitative polymerase chain reaction. Using a linear mixed effects model, the power to detect transcriptional changes corresponding to active and inactive Crohn's disease was calculated.

Results

Total simple endoscopic score for Crohn's disease score corresponds with expression of most inflammatory biomarkers. For most genes, 2 to 5 biopsies are needed to reduce sampling error to <25% for most genes. To measure changes in mRNA expression corresponding to active versus inactive Crohn's disease, 1 to 2 intestinal biopsies from 3 patients before and after treatment are needed to yield power of at least 80%.

Conclusions

Measuring proinflammatory gene expression from mucosal biopsies from patients with Crohn's disease is practicable and provides objective biomarkers that can be used in proof-of-concept and mechanism-of-action trials to assess response to therapy.