Over the last two centuries electrical microstimulation has been often used to demonstrate causal links between neural activity and specific behaviors or cognitive functions. It has also been used successfully for the treatment of several neurological disorders, most notably, Parkinson's disease. However, to understand the mechanisms by which electrical microstimulation can cause alternations in behaviors and cognitive functions it is imperative to characterize the cortical activity patterns that are elicited by stimulation locally around the electrode and in other functionally connected areas.
To this end, in a new study published in the December, 2005, issue of Neuron, Andreas S. Tolias and Fahad Sultan, under the guidance of Prof. Nikos K. Logothetis from the Max Planck Institute for Biological Cybernetics in TÃ¼bingen, have for the first time developed a technique to record brain activity using the blood oxygen level dependent (BOLD) signal while applying electrical microstimulation to the primate brain. They found that the spread of activity around the electrode in macaque area V1 is larger than expected from calculations based on passive spread of current and therefore may reflect functional spread by way of horizontal connections. Consistent with this functional transsynaptic spread they also obtained activation in expected projection sites in extrastriate visual areas demonstrating the utility of their technique in uncovering in vivo functional connectivity maps.
Using the microstimulation/MRI technique in conscious, alert primates holds great promise for determining the causal relationships between activation patterns across distributed neuronal circuits and specific behaviors. Finally, this method could also proof useful in understanding and optimising the method of intra-cranial electrical stimulation in the treatment of neurological diseases.