The human brain is an intricate organ, responsible for everything we think, feel, and do. Understanding how this complex network functions, how its regions interact, and how connections are formed is a key scientific pursuit. Observing brain activity and mapping its connections is important for advancing knowledge of neurological disorders, developing new treatments, and understanding cognition. Various techniques allow scientists to study this organ.
Observing Brain Activity from Outside
Scientists can observe brain activity without needing to enter the skull, using methods that detect signals from outside. Electroencephalography (EEG) measures electrical signals generated by neurons in the brain. Electrodes placed on the scalp detect these impulses, appearing as brain waves, providing information about brain states like sleep or alertness. EEG is also widely used to diagnose conditions such as epilepsy, as it can pinpoint abnormal electrical activity. It offers excellent temporal resolution, detecting changes in brain activity quickly, within milliseconds.
Functional Magnetic Resonance Imaging (fMRI) is another non-invasive method that identifies brain activity by tracking changes in blood flow. When a brain region becomes more active, it requires more oxygen, increasing blood flow to that area. fMRI detects these subtle changes in blood oxygenation, providing detailed images of activity within the brain. This technique excels in spatial resolution, allowing researchers to pinpoint specific brain regions involved in various cognitive processes. It is a powerful tool in cognitive neuroscience to understand which brain parts are engaged during tasks like memory or decision-making.
Peeking Inside with Specialized Tracers
For deeper insights into brain function and connectivity, some techniques introduce specialized “tracers” into the body.
Positron Emission Tomography (PET) uses radioactive tracers, often a glucose analog, injected into the bloodstream. More active brain cells consume more glucose; the PET scanner detects positrons emitted by the tracer in these metabolically active regions. This allows researchers to visualize areas of high or low metabolic activity, useful for diagnosing conditions like Alzheimer’s disease or certain cancers by revealing altered metabolic patterns.
Neuroanatomical tract-tracing techniques map the physical connections between neurons. These methods involve injecting tracer substances into specific brain regions. The tracers are then transported along neuronal pathways, either from the cell body down the axon (anterograde tracing) or from the axon terminal back to the cell body (retrograde tracing). This transport reveals the intricate “wiring” of the brain, showing how different brain areas communicate with each other. These techniques are important in neuroscience research for understanding the complex circuits that underlie brain function.
Direct Access: Invasive Monitoring
For precise measurements, especially in clinical or specific research settings, invasive techniques involve direct electrode placement on or within brain tissue.
Electrocorticography (ECoG) involves placing electrode grids directly on the brain’s surface, underneath the skull. This method provides high spatial and temporal resolution compared to scalp EEG, allowing detailed observation of electrical activity. ECoG is used in pre-surgical mapping for epilepsy patients to locate seizure-generating areas before surgery.
Local Field Potentials (LFPs) are recorded by inserting microelectrodes directly into brain tissue. These electrodes measure the summed electrical activity of a population of neurons in a localized area. LFP recordings offer fine-grained detail about neuronal network dynamics within specific brain regions. While highly invasive and typically limited to animal research, LFP provides insights into how groups of neurons interact and process information at a microscopic level.