Introduction to Brain Imaging and Neuroscientific Discovery
Tools of Discovery and Brain Localization
Mind-Brain Relationship:
The mind seeking to understand the brain is among the ultimate scientific challenges.
Paraphrasing cosmologist John Barrow: A brain simple enough to be fully understood is too simple to produce a mind able to understand it.
Thinking occurs by releasing billions of neurotransmitter molecules across trillions of synapses.
A central conclusion among neuroscientists is that the mind is what the brain does.
History of Brain Mapping:
For most of human history, scientists lacked tools that were high-powered yet gentle enough to reveal the activity of a living brain.
Early case studies provided initial evidence for brain function localization:
Damage to one side of the brain often caused numbness or paralysis on the opposite side of the body, indicating that the right side of the body is wired to the left side of the brain and vice versa.
Damage to the back of the brain disrupted visual processing.
Damage to the left side of the brain produced speech difficulties.
Modern Techniques for Eliciting and Observing Brain Activity:
Selective Lesioning: Scientists can selectively destroy or damage tiny clusters of brain cells to observe functional outcomes.
Stimulation: Scientists can stimulate various brain regions electrically, chemically, or magnetically and note the resulting behavioral or experiential changes.
Effects of Regional Brain Stimulation: Depending on the specific area stimulated, individuals may giggled, hear voices, turn their head, feel as though they are falling, feel less depressed, or experience an out-of-body state.
Single Neuron Recording: Microelectrodes with tips small enough to detect an electrical pulse in a single neuron allow researchers to monitor neuronal messaging (e.g., detecting where information travels in a rat's brain when its belly is tickled).
Detecting Brain Activity and Neuroimaging Techniques
Biological Signals:
Mental activity emits electrical, metabolic, and magnetic signals that allow neuroscientists to observe the active brain.
Electrical activity across billions of neurons sweeps in regular waves over the brain's surface.
Lesioning:
Definition: Tissue destruction or brain damage.
Causes: Occurs naturally via disease or surgical trauma, or experimentally using microelectrodes to destroy brain cells.
Electroencephalogram (EEG):
Definition: An amplified recording of electrical activity waves sweeping across the brain's surface.
Mechanism: Electrodes embedded in a shower cap-like hat and coated with conductive gel are placed on the scalp to measure electrical waves.
Sample Finding: Symptoms of depression and anxiety correlate with increased electrical activity in the right frontal lobe, a brain area associated with behavioral withdrawal and negative emotion.
Positron Emission Tomography (PET):
Definition: A neuroimaging technique that displays where a radioactive form of glucose goes while the brain performs a given task.
Fuel Consumption Context:
Active neurons consume sugar glucose as chemical fuel.
Although the human brain accounts for only about of total body weight, it consumes of total calorie intake.
Mechanism:
The individual receives a temporarily radioactive glucose tracer.
The scan tracks gamma rays emitted by this glucose tracer during task performance.
Functions similarly to weather radar tracking rain; hotspot visual displays show the most active brain regions during mathematical calculations, viewing images of faces, or daydreaming.
Sample Finding: Monkeys with an anxious temperament possess brains that consume higher amounts of glucose in regions tied to fear, memory, and expectations of reward and punishment.
Magnetic Resonance Imaging (MRI):
Definition: A technique using magnetic fields and radio waves to generate computer-produced images of soft tissue, displaying brain structure, size, and shape.
Mechanism:
The head is placed inside a strong magnetic field, aligning the spinning atoms of brain tissue molecules.
A radio wave pulse momentarily disorients these atoms.
As the atoms return to their typical spin, they emit signals that create detailed structural maps of soft tissue.
Diagnostic Findings:
Reveals a larger-than-average neural area in the left hemisphere among musicians who display perfect pitch.
Reveals smaller-than-average brain regions enabling word comprehension in individuals diagnosed with a reading disability.
Reveals enlarged ventricles (fluid-filled brain areas) in some individuals diagnosed with schizophrenia.
Sample Finding: Individuals with a history of violence tend to exhibit smaller frontal lobes, particularly in regions responsible for moral judgment and self-control.
Functional Magnetic Resonance Imaging (fMRI):
Definition: A specialized application of MRI that reveals both brain function and structure by comparing successive, continuous MRI scans.
Mechanism:
Detects blood flow and oxygenation changes: Increased blood and oxygen flow directly support active brain regions and neural networks.
Example: Detects blood rushing to the back of the brain (visual cortex) when visual scenes are processed.
Findings on Brain Adaptation:
Neural Energy Conservation: When macaque monkeys viewed repeated images over a period of weeks, fMRI detected reduced oxygen, lead, and blood flow sent to the visual cortex when viewing familiar images.
Emotional and Task Mapping:
Maps active brain regions during pain, rejection, listening to angry voices, thinking about frightening stimuli, feeling happiness, or experiencing sexual arousal.
Mind Reading Capabilities:
In a study scanning the brains of participants completing distinct mental tasks (e.g., reading, gambling, rhyming), researchers identified the specific mental activity being performed with accuracy.
Sample Finding: Years after surviving a near plane crash, passengers reviewing trauma-related material displayed heightened activation in the brain's fear, memory, and visual centers when watching footage related to the terrorist attacks.
Functional Near-Infrared Spectroscopy (fNIRS):
Definition: A portable technique that shines infrared light through the scalp onto blood molecules to identify regional brain activity.
Advantage: Equipment fits inside a large backpack, allowing researchers to study the biology of the mind in difficult-to-reach populations.
Neuroimaging Critique and Large-Scale Initiatives
Neurohype and Neuroskepticism:
Individuals rate scientific explanations as significantly more believable and interesting when they contain neuroscience images.
Vivid scan visualizations do not mean brain regions literally light up.
Neuroskeptics warn against overblown claims regarding the ability of scans to predict consumer choices, detect lies, or foretell criminal behavior.
Commercial and applied claims regarding neuromarketing, neuroleadership, neurolaw, and neuropolitics often constitute hype.
Because all human experience is brain-based, regional activation during everyday tasks (e.g., listening to a lecture vs. feeling lust for a lover) is expected.
Global Research Initiatives:
Current techniques peering into the brain are doing for psychology what the microscope did for biology and the telescope did for astronomy.
The European Human Brain Project is a research initiative aimed at understanding brain structure and function.
Developmental Initiatives: Research projects are tracking brain development across the lifespan from ages to .
Longitudinal Child Study: A massive study is following over young children through adolescence to map neurological development.
International Collaboration: These projects harness hundreds of scientists across dozens of countries.
Paraphrasing Aristotle: Individually, single researchers contribute little or nothing directly to the absolute truth, but through the union of all, a considerable amount of knowledge is amassed.
Summary Matrix of Common Neural Measures
Electroencephalogram (EEG):
Operational Mechanism: Electrodes placed on the scalp measure electrical activity across neurons.
Key Finding: Anxiety and depression symptoms correlate with heightened activity in the right frontal lobe (associated with negative emotion and behavioral withdrawal).
Positron Emission Tomography (PET):
Operational Mechanism: Tracks regional uptake of a temporarily radioactive form of glucose during task execution.
Key Finding: Anxious monkeys show elevated glucose consumption in fear, memory, and reward/punishment processing networks.
Magnetic Resonance Imaging (MRI):
Operational Mechanism: Utilizes magnetic fields and radio waves to construct structural maps of soft tissue.
Key Finding: Individuals with violent histories tend to have reduced frontal lobe volume, specifically in regions mediating moral judgment and self-control.
Functional Magnetic Resonance Imaging (fMRI):
Operational Mechanism: Measures blood flow and oxygenation levels to brain regions by comparing continuous MRI scans to evaluate functional activity.
Key Finding: Near plane crash survivors reviewing trauma materials displayed increased activation in fear, visual, and memory centers when viewing footage years after the incident.