The proposed research is a direct extension of the research carried out in the previous 3 years. The capacity of magnetoencephalography (MEG) in identifying active tissues in the porcine brain will be evaluated in order to establish a solid empirical basis for interpreting MEG signals from gyrencephalic brains including the human brain. We will determine the subcortical generator responsible for the novel somatic evoked field (SEF) found to be generated by a structure deeper than the thalamus. This generator appears to be the spinal division of the trigeminal -nuclei that carries nociceptive information. If so, we will be demonstrating a capability of MEG with important clinical applications, i.e., the capability of detecting subcortical activities related to pain. Field potentials within the brain associated with this response were quite distinct from those associated with presumably cutaneous responses. We will use mechanical and electrical stimuli to stimulate the cutaneous and nociceptive pathways, and verify the differences in the pathways activated with depth recordings. The cortical areas receiving projections from these two pathways will be found with MEG and ECoG. Our ablation results indicated that the three areas (two areas in the primary somatosensory area (51) and one area in the secondary somatosensory area, 511) can be distinguished with MEG. We will also test whether multiple areas of activation found within the coronal 51 area correspond to areas 3b, 1 and 2 of the primate. In addition to the study of cortical projections from the peripheral afferents, we will study the cortico-cortical connections to determine whether MEG is useful for measuring such connections. The connections between the cortical areas identified from the above study will be investigated by electronically stimulating one area and recording induced activities in connected cortical areas within and across the hemispheres. Our MEG sensor is sensitive enough to record induced, time-locked by phase-unlocked cortical responses during single epochs from a specific cortical areas. Thus, we expect to be able to study the cortical connections. If this is feasible, we will be demonstrating a new capability of MEG for studying brain functions. Finally, we will use MEG to estimate the size of active tissue from the magnitude of SEF for early cortical responses and also by applying a linear estimating algorithm which has been shown to be capable of estimating not only size but also shape of active tissue in a sulcus on stimulated data. If this is the case for empirical data, we can demonstrate that size and perhaps shape of active tissue may be estimated with MEG.
Showing the most recent 10 out of 20 publications
