The Brain

The Tools of Discovery: Having Our Head Examined

Your mental activity is constantly giving off electrical, metabolic, and magnetic signals that allow neuroscientists to observe your brain at work.

Recording the Brain's Electrical Activity:

- Electroencephalogram (EEG) is a readout of the brain's regular neurons that sweep in waves across its surface (photo 1)

- CT (computed tomography) scan takes x-ray photos that can reveal brain damage (photo 2)

-During a PET (positron emission tomography) scan, a person receives temporarily radioactive glucose which appears as "hot spots" to show brain activity (photo 3)

-MRI (magnetic resonance imaging) provides a detailed picture of the brain's soft tissue

-fMRI (functional MRI) reveals the brain's functioning as well as its structure

Older Brain Structures

The brainstem is the oldest and innermost region of the brain. It begins where the spinal chord enters the skull, at the medulla. The medulla controls heartbeat and breathing. Above the medulla is the pons, which helps coordinate movements.

Above the pons is the reticular formation, which plays a big role in controlling arousal. The thalamus sits at the top of the brainstem and is the sensory switchboard.

The cerebellum, known as the "little brain" has a lot of functions including processing sensory input and coordinating movement and balance.

The limbic system is a neural system composed of the hippocampus, amygdala, and hypothalamus. It is located below the cerebral hemispheres and is associated with emotions and drives.

The amygdala is linked to emotion. The hypothalamus directs several maintenance activities (eating, drinking, and body temperature), helps govern the endocrine system via the pituitary gland, and is linked to reward and emotion. The hippocampus is linked to memory.

The Cerebral Cortex

The cerebral cortex is a thin surface layer of interconnected neural cells covering the cerebral hemispheres, and is the body's ultimate control and information-processing center.

The cortex is supported by the glial cells, which are cells in the nervous sytem that support, nourish, and protect neurons. Each hemisphere of the cortex is divided into four lobes:

- Frontal lobes: behind the forehead; involved in speaking and muscle movements and in making plans and judgments

-Parietal lobes: at the top and to the rear; receives sensory input for touch and body position

-Occipital lobes: at the back of your head; receives information from the visual fields

-Temporal lobes: just above the ears; includes auditory areas, each receiving information primarily from the opposite ear

The motor cortex is an area at the rear of the frontal lobes that controls voluntary movements. The sensory cortex is the area of the front of the parietal lobes that registers and processes body touch and movement sensations.

The association areas are areas of the cerebral cortex that are not involved in primary motor or sensory functions, but are involved in higher mental functions such as learning, remembering, thinking, and speaking.

Association areas are found in all four lobes. In the frontal lobes, they enable judgment, planning, and processing of new memories. Phineas Gage famously damaged his frontal lobe in a railroad work accident. From this damage, his mental abilities and memories were still intact, but his personality completely changed. He was once soft-spoken but now became irritable and he completely lost his morals.

Aphasia is an impairment of language, usually caused by left hemisphere damage either to Broca's area (impairing speaking) or to Wernicke's area (impairing understanding).

The brain has plasticity that allows it to change, especially during childhood, by reorganizing after damage or by building new pathways based on experience. The formation of these new neurons is called neurogenesis.

Our divided Brain

The brain has two hemispheres, which each have their own different functions.

The hemispheres are connected by a large band of neural fibers called the corpus callosum. This carries messages between the two hemispheres.

By cutting the corpus callosum, the brain's two hemispheres are isolated from one another, also known as a split brain.

Right-Left Differences in the Intact Brain

When a person performs a perceptual task, for example, brain waves, bloodflow, and glucose consumption reveal increased activity in the right hemisphere. When the person speaks or calculates, activity increases in the left hemisphere.

The Brain and Consciousness

Consciousness is our awareness of ourselves and our environment.

Cognitive neuroscience is the interdisciplinary study of the brain activity linked with cognition (including perception, thinking, memory, and language). Most cognitive neuroscientists are exploring and mapping the conscious functions of the brain cortex.

Dual processing is the principle that information is often simultaneously processed on separate conscious and unconscious tracks.

A visual perception track enables us to create the mental furniture that allows us to think about the world- to recognize things and plan future actions. A visual action track guides our moment-to-moment actions.

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