Brain Imaging: Observing Ongoing Neural Activity

Abstract The neuroimaging techniques available to observe ongoing brain activity during human cognition include functional magnetic resonance imaging, positron emission tomography, event‐related potentials, magnetoencephalography and event‐related optical signalling. Brain activity can be disrupted temporarily via transcranial magnetic stimulation. In addition, brain structures and their connectivity can be seen via magnetic resonance imaging and diffusion tensor imaging. Using these neuroimaging methods, both spatial and temporal precision, and structural and functional connectivity are attainable in describing the underlying neural substrates that comprise human cognition. Significant progress has been made in understanding the physiological basis of human thought with many exciting new frontiers opening up including understanding the genetics of human cognition and the neural basis of consciousness. Key Concepts The integration of structural and functional neuroimaging allows for the localisation of neural areas responsible for specific mental operations. Computed tomography's low image resolution restricts its utility when studying specific neural anatomy. Magnetic resonance imaging procedures a high‐resolution structural image in a noninvasive manner that is now the standard for structural imaging. Diffusion tensor imaging utilises diffusion of water molecules across white matter to map structural connectivity of neurological regions. Functional imaging provides methods of assessing specific brain operations by indirectly measuring the physiological changes that occur during cognition. Event‐related potentials measure relative changes in electrical activity of groups of neurons through electrodes located on the scalp and provides measures of neural activity with high temporal resolution. Magnetoencephalography measures small changes in magnetic signals generated when neurons fire and provides a high degree of temporal accuracy, yet is limited to neurons firing in the most superficial brain regions. Functional data of neural activity during a control condition is often subtracted from functional data of neural activity during an experimental condition to determine activated brain regions. Transcranial magnetic stimulation is used to interfere with neuronal signalling constrained to the surface of the cortex, to help determine the mental computation at that specific location and to reveal the necessary neural tissue. The use of diverse measures of neural function continues to transform the capacity to understand the roots of cognitive function.