|Programm||"Degeneration und Regeneration– Grundlagen, Diagnostik und Therapie"|
Functional MRI in Monkeys: Imaging, Connectivity & Electrophysiology Investigations Using a High-Field Scanner
Logothetis N. K.
In the first part of my talk Ill describe applications of spatially resolved fMRI, including imaging with implanted RF coils. In the second part, Ill described experiments in which we simultaneously traced manganese chloride and wheat-germ-agglutinin conjugated to WGA-HRP to evaluate the specificity of the former by tracing the neuronal connections of the basal ganglia of monkeys. By showing the sequential transport of Mn2+ from striatum to pallidum-substantia nigra and then thalamus, we demonstrated MRI visualization of transport across at least two synapses. Finally, I shall present results on the neural basis of the BOLD signal. We found that visual stimulation causes a significantly stronger increase in the local field potentials (LFPs_ than in the multiunit activity (MUA), and that the former predict the fMRI responses better than the latter. LFPs represent slow waveforms, including synaptic potentials, afterpotentials of somato-dendritic spikes, and voltage-gated membrane oscillations. Such waveforms reflect both the input of a given cortical area and its local intracortical processing, including the activity of excitatory and inhibitory interneurons. MUA represents mostly the spiking of neurons, with single-unit recordings mainly reporting on the activity of the projection neurons that form the exclusive output of a cortical area. Thus, the fMRI signal is better correlated with the inco