How Does Neuroscience Investigate Intelligence?

Neuroscience measures intelligence across various possible biological factors:

• Head Size or Brain Size. In the early times, people used to believe that a large head houses a big brain. If knowledge is stored in the brain, then a large brain can store more information, right? Not necessarily. There's not much correlation between head size or brain size and intelligence (as measured by intelligence tests). In fact, head size is more correlated to the body's built. However, interest in this area brought significant findings. Other properties of the brain may be more related to intelligence than the mere size of the brain. These properties include the quantity of neurons in the brain, myelination, and the number of creases of the brain.
• Information-Processing Speed. The structuralist approach in early Psychology attempted to measure mental processes by quantifying reaction time. The basic question is: How quick does the brain process and react on the information sent forth by our senses? Interestingly, information-processing speed has significance correlations with traditional intelligence tests. For example, talented musicians tend to be sensitive sound variations and patterns.
• Electrical Activity in the Brain. When MRIs and EEGs were developed, neuroscience went further in assessing information-processing speed by measuring how the brain actually processes information. Specifically, it measures nerve conduction velocity (NCV), or the speed of neural transmission within the neuron and across synapses. Sensory stimulus evokes electrical potential in a neuron through its dendrites; thus, NCV within the neuron is measured by the speed of electrical conductance from the neuron's dendrites, to the cell body, the axon, and the terminal buttons. On the other hand, NCV across synapses is measured by how fast neurotransmitters travel from the terminal buttons to the receiving neuron's dendrites. Brain electrical activity is also interestingly correlated with traditional intelligence scores, although some studies show inconsistent results.
• Energy Consumption in the Brain. When neuroscientists learned that nerve cells consume energy like other body cells, they had this curious hypothesis that a "working" brain consumes more energy than a "lazy" brain. As soon as PET scans became available, neuroscientists studied how extensive and fast brains consume and break down glucose (a type of sugar). Research shows that the higher the intelligence score of a person is, the more glucose the brain consumes when at rest when performing any cognitive activity the person chooses, and the less glucose the brain consumes when performing assigned cognitive tasks. Thus, it is believed that intelligent people are capable of utilizing extensive or massive brain power and can use this power in effective ways.