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Remove mazaika4/5/2023 ![]() 2004), as well as issues pertaining to radio frequency (RF) noise, animal movement during scanning, motivation to perform specific behavioral tasks, environmental constraints for these tasks, etc. These include the need to refrain from use of metallic material near the head, even if non-magnetic due to potential eddy current artifacts ( Bernstein, King, et al. Some aspects are general to animal neurophysiology studies- need for restraint, training, behavioural monitoring, etc.-while other aspects are unique to performing studies in the MRI scanner. However, a number of challenges must be overcome to carry out a successful awakebehaving macaque fMRI study. (2010)-that study was made possible by the fact that the projections of the LGN to the cortex are well known in the monkey.įunctional MRI in awake-behaving macaques thus affords us the possibility of studying primate brain function in a well-defined model (i.e., well-defined structure and connectivity) and to perturb the cortex using causal manipulations such as temporary deactivation, electrical microstimulation, or optogenetic manipulation ( Boyden, Zhang et al. This hypothesis had not been directly tested, until Schmid et al. The anatomical basis for blind-sight has long been hypothesized to be the branching connections of the lateral geniculate nucleus of the thalamus (LGN) to other visual areas-in other words, while the V1 input to the cortical visual hierarchy is lost following ablation of V1, other visual areas receive indirect input via the thalamus. (2010) used fMRI in awake-behaving macaques to demonstrate the neural basis for blind-sight-the residual visual capacity following loss of primary visual cortex (see ( Leopold 2012 for a review). For example, recently Schmid, Mrowka et al. In monkeys, this data has provided for a rich map of connectivity that can not only aid us in interpreting single-cell and fMRI results, but also formalize relationships between brain regions that can then be tested directly with temporary deactivation. Axonal tracing requires local injection of a tracer molecule followed by death and histological analysis, all of which is ethically infeasible in humans. Studying brain function in humans alone is also limiting in that very little is known about the structure of the human brain-at least when compared to what we know about the macaque brain, for example. ![]() 2009) in the monkey do not exist for human imaging, and direct microstimulation or temporary deactivation by cortical infusion in a normal human subject is ethically unthinkable. ![]() 2010) and local electrical microstimulation ( Tolias, Sultan et al. While some coarse techniques exist to manipulate human brain function, such as transcranial magnetic stimulation, non-invasive methods comparable to localized chemical deactivations ( Liu, Yttri et al. In order to draw causal links between brain function and behavioural performance, it is necessary to directly alter the brain either prior to or during fMRI. While human fMRI can go a long way to answering fundamental questions about organization of function in the brain, much of the information we obtain from fMRI is correlative-for example, while activity in an area may correlate with a task, it is impossible to assume that the activity causesthe observed behaviour. The combination of non-invasiveness and the broad availability of equipment and tools to perform fMRI have made this technique popular and broadly adopted. Well-developed commercial MRI systems with built-in support for functional imaging are widely available, as are a plethora of tools, both free and commercial, for the analysis of human functional brain images. The technique allows for noninvasive whole-volume measurements of brain function in humans and repeatable non-invasive measurement of activity over the whole brain, providing a correlate of neural activity without use of tracers or electrodes. ![]() Functional magnetic resonance imaging (fMRI) is perhaps the most important development in the measurement of human brain function in recent neuroscience history.
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