Imaging regional changes in the spontaneous activity of the brain: an extension of the minimum-norm least-squares estimate.

This paper describes methods for inferring mathematically unique local distributions of primary cortical current that underly changes in the average pattern of power of the ongoing ("spontaneous") extracranial magnetic field of the brain. In previous work we demonstrated that mathematically unique solutions to the inverse problem are possible for current sources of the brain's field, without assuming a small set of current dipoles as a source model. In principle, it is possible to locate and delineate patterns of current of any configuration. In practice this approach applies to synchronized neuronal activity, e.g., activity which is known to underly average evoked or event-related brain responses. This paper extends that approach to local changes in incoherent activity, e.g., activity yielding fields or potentials that tend to be self-cancelling when averaged over time. This includes the spontaneous brain activity normally treated as background noise when it accompanies event-related responses. We demonstrate that local changes in this ongoing incoherent activity may also be uniquely delineated in space and time. The solution is a covariance matrix characterizing activity across an image surface. Its diagonal elements represent the spatial pattern of mean current power. Evidence is reviewed indicating that the distribution of the brain's magnetic field, due to both its synchronized and incoherent neural activity, is affected by early sensory-perceptual processes and by higher cognitive processes. Hence, in principle, the ability to delineate both kinds of sources in space and time makes it possible to form more comprehensive dynamic functional images of the human brain.

In vitro cultivation of an African strain of Babesia bigemina, its characterisation and infectivity in cattle.

An African (Kenyan) strain of Babesia bigemina, Muguga (B(2-1)), was inoculated into a calf from a stabilate and blood from the calf was used to establish the parasite in vitro. The strain has been cultured continuously for 20 months, initially in bovine erythrocytes with 60% adult bovine serum, later, with 50%. Cultures were incubated at 37 degrees C in RPMI 1640 medium with a gas mixture of 1% O2, 5% CO2, 94% N2. Adaptation in vitro was demonstrated when serum from a calf which had recovered from infection with B(2-1) bound to proteins of Mr 46 kDa, 49 kDa, 52 kDa, 61 kDa and 72 kDa on Western blots of B(2-1) antigens from cattle blood but did not recognise the 49 kDa or 52 kDa antigens from in-vitro-derived parasites. These proteins were considered specific for B(2-1), as they were not recognised by the same serum on profiles of a Mexican isolate of B. bigemina or an African isolate of B. bovis (Kwanyange). After 9 months of in vitro culture, a stabilate of the cultured parasite was injected into two splenectomised calves and one intact calf. The calves experienced a drop in packed cell volume and low parasitaemias but recovered spontaneously. Two of these animals, one splenectomised and one intact, were challenged with virulent B(2-1) and experienced only mild babesiosis, in contrast to a previously uninfected calf also challenged with B(2-1), which had to be euthanised after 5 days with severe babesiosis.