Department High-field Magnetic Resonance
I am interested in studying the neural processes that underly volitionally regulated hemodynamic signals. To investigate these mechanims, I use simultaneous intra-cortical microelectrode recordings and epidural functional near-infrared spectroscopy. We use this technique to study local neurovascular coupling in non-human primates.
Neural correlates of volitional BOLD regulation in primates
Animals can learn to alter their brain activity when provided with feedback, as shown by some of the first studies in the field by one of our collaborators (Fetz et al., 1969, 1971). Later studies have further reiterated that animals and people can learn self-regulation of the brain signals through instrumental training with contingent feedback and reward (Cerf et al., 2010, Kobayashi et al., 2010). A recent study shows that rodents can learn to control the pitch of an auditory cursor to reach one of two targets by modulating activity in primary motor cortex irrespective of physical movement (Koralek et. al. 2012). Recently, real-time functional Magnetic Resonance Imaging (fMRI) has been developed for simultaneous measurement and observation of blood oxygenation-level dependent (BOLD) activity of the brain during an ongoing task. An innovative application of this technique is the possibility to train individuals to learn volitional control of localized brain activity using neurofeedback protocols. Recent studies in our group (Sitaram et al., 2011, Caria et al., 2011, Caria et al., 2007 and 2010, Rota, Sitaram et al., 2009 and 2010, Ruiz et al., 2011) and elsewhere (deCharms et al., 2007) have shown evidence that healthy volunteers as well as patients can learn to volitionally regulate circumscribed brain regions, and that this learned regulation correlates with behavioral changes in the perception of emotional, linguistic or pain-related stimuli. These studies have indicated that real-time functional Magnetic Resonance imaging could be used as a powerful tool to change brain signals in targeted regions and circuits as an independent variable to study the effect of brain signal changes on behavior and cognition.
In spite of these developments, a causal link between volitional regulation of the BOLD signal and respective changes in neural signals of the same brain region have not yet been established. It is still not clear whether learned changes in BOLD activity of local brain regions accurately reflect neuro-electric changes, resulting in a specific activation of local neuronal ensembles, or, whether a control mechanism is established through conditioning that allows for direct control of the local blood vessels. In the absence of such evidence one may argue that learned changes in the BOLD signal are due merely to changes in blood flow or metabolism, and are potentially decoupled from any signal of neural origin. If this is indeed the case, this would call into question whether self-modulated fMRI signals reliably reflect specific local neuronal activity and continue throughout the learning process. If not, the basis of ongoing studies addressing the question whether the self-regulation process can make use of high spatial specificity of the BOLD signal by using high spatial resolution may be lost.
To address the above problem, I intend to perform reward training of a circumscribed region in the brain of non-human primates until successful self-regulation is achieved, followed by simultaneous electrophysiological recordings of the neurons in the same brain region during the self-regulation.