Search

Magnetic field tomography is a technique for extracting 3-dimensional estimates of current density in the brain, from non-contact, non-invasive measurements of the magnetic field generated by the brain. It allows visualisation of both cortical and subcortical focal activation patterns at millisecond intervals, and the relative time difference between active cortical areas. We have used this technique to study the activation history of discrete brain regions associated with the preparation for, initiation and inhibition of movement, and movement itself in a CNV paradigm. The strongest focal activities are found within well defined cortical regions, namely the auditory (A1), sensorimotor (SM1), medial parietal area (MPA) and anterior supplementary motor area (SMA). For the movement condition, activation history differs for the warning stimulus and the stimulus initiating movement.

A series of elderly patients with dementia of Alzheimer type (AD), multi-infarct dementia (MID) and functional (non-organic) psychiatric illness (major depressive disorder) were selected by DSM III-R criteria and had the following investigations: a battery of cognitive tests, EEG with power and coherence spectral analyses of T4-T6, T3-T5, P4-O2, P3-O1 channels, visual evoked potential (flash and pattern reversal) and P300 recordings as well as single photon emission tomography (SPECT) using 99mTc HMPAO. Three subsets of patients were chosen on clinical and SPECT criteria. These were as follows: patients with a clinical diagnosis of AD and a SPECT rCBF pattern showing bilateral temporo-parietal perfusion deficits (AD type), patients with a clinical diagnosis of MID and a SPECT rCBF pattern showing single focal perfusion deficits or multiple areas of low perfusion in the cerebral cortex suggestive of ischaemic change (MID type SPECT picture) and functionally ill patients with normal rCBF (controls). The AD type group differed from the MID rCBF group in having significantly less alpha and more delta 2 (2- < 4 Hz) power. The latter had significantly lower alpha power than the controls. The 2 dementia groups with abnormal rCBF patterns did not differ in terms of coherence spectra or P300 latencies, but both had lower within and between hemisphere alpha coherence values and longer P300 latencies than the "controls" with normal rCBF. There were no group differences in the flash VEP P2-pattern reversal P100 latency difference values.

Elderly patients with senile dementia of the Alzheimer type (SDAT), multi-infarct dementia (MID) and functional psychiatric illness, along with elderly control subjects, were studied longitudinally at 6 monthly intervals over a 2 year period, with cognitive testing and EEG power spectral analyses being carried out on each occasion. There was no significant change in the EEG power over time although a significant regression effect was noted for cognitive performance in the SDAT group. A number of between-group differences were apparent. The SDAT patients had more delta and theta power and less alpha power than those with MID and the latter group had a higher percentage of delta and theta power than the functional patients. The functional patients and normal subjects were differentiated from each other by a number of EEG power variables. The implications of these findings with respect to differential diagnosis in geriatric psychiatry are discussed.

Serial visual evoked potentials to flash and pattern reversal stimuli were recorded in elderly patients with senile dementia of the Alzheimer type (SDAT), multi-infarct dementia (MID) and functional psychiatric illness, and in a group of elderly control subjects. Recordings were made at 6 monthly intervals over a 2 year period. Latency and amplitude of the main components were measured and the flash P2-pattern reversal P100 latency difference value was calculated. In all groups significant changes over time did not occur for any parameters but in the SDAT group the regression coefficient for the latency of the flash P2 component and the flash P2-pattern reversal P100 latency difference was significant, reflecting a trend towards increasing flash P2 latency as time progressed. The flash P2-pattern reversal P100 latency difference was longer in the SDAT and MID groups than in the functional patients, confirming the findings of previous reports. The latency difference in the SDAT group only was significantly greater than that in the control group.