Chapter 2The Brain

The Brain

Technology to Study the Brain

• Electroencephalograph (EEG): • records “waves” of electrical activity in the brain using metal electrodes

• Computerized axial tomograph (CAT):• thousands of X-ray photos of the brain are combined to form a cross-

sectional picture

• Magnetic resonance imaging (MRI):• produces three-dimensional images of the brain’s soft tissues by

detecting magnetic activity from nuclear particles in brain molecules

Technology to Study the Brain

• Positron emission tomography (PET): measures neural activity in different brain regions over several minutes by monitoring sugar glucose consumption

• Functional magnetic resonance imaging (fMRI): measures neural activity in different brain regions averaged over seconds by monitoring blood oxygen levels

PET Scan

MRI Scan

Three Major Brain Regions

• Their names come from their physical location in the human embryo.

– Hindbrain: Located above the spinal cord,

– Midbrain: Located above the hindbrain– Forebrain: Located above the midbrain

Development of the Brain

Three Major Brain Regions: Hindbrain

• Hindbrain consists of:

– Medulla: controls breathing, heart rate, swallowing, digestion, and posture

– Pons: associated with sleep and arousal

– Cerebellum: regulates and coordinates body movement and may play a role in learning

The Cerebellum

Midbrain

Reticular formation: regulates and maintains consciousness

– plays an important role in controlling arousal

Forebrain

Controls complex emotional reactions, cognitive processes, and movement patterns. Consists of: – Thalamus: the brain’s sensory relay station

– Limbic system: influences fear, aggression, and new memories

– Cerebral cortex: located on top of these structures; the most complex part of the brain

Thalamus

• Brain’s Sensory Switchboard

• Directs incoming information from the sensory systems (except smell) to the appropriate location on the cortex.

The Brainstem and Thalamus

• a doughnut-shaped system of neural structures at the border of the brainstem and cerebral hemispheres

• associated with emotions such as fear and aggression and drives such as those for food and sex

• includes the hypothalamus, hippocampus and amygdala

Limbic System

The Limbic System

Hypothalamus

• neural structure lying below (hypo) the thalamus

• directs several maintenance activities• eating• drinking• body temperature

• helps govern the endocrine system via the pituitary gland

• linked to emotion

Hippocampus

• Structure linked to the processing/formation of new explicit memories

• Manufactures new neurons

Amygdala [ah-MIG-dah-la]

– two almond-shaped neural clusters that are components of the limbic system and are linked to emotion, especially rage and fear

The Limbic System• Electrode implanted in reward center

Main Parts of the Human Brain

Lobes of the Cerebral Cortex

• The cerebral cortex is divided into two rounded halves, called the cerebral hemispheres.

– These hemispheres are connected together at the bottom by the corpus callosum.

– Both hemispheres are divided into four major sections called lobes:

The Brain

The Cerebral Cortex

Cortical Localization

• Occipital Lobes

– include the visual areas, each of which receives visual information from the opposite visual field

• Temporal Lobes

– include the auditory areas, each of which receives auditory information primarily from the opposite ear

Visual Cortex

• Functional MRI scan of the visual cortex activated by light shown in the subject’s eyes

Visual and Auditory Cortex

Cortical Localization

• Frontal Lobes– involved in speaking and muscle

movements and in making plans and judgments

• Parietal Lobes

– include the sensory cortex

The Cerebral Cortex

The Cerebral Cortex• Motor Cortex

– area at the rear of the frontal lobes that controls voluntary movements

• Sensory Cortex– area at the front of the parietal lobes

that registers and processes body sensations

Association Areas• Areas of the cerebral

cortex that are not involved in primary motor or sensory functions

• Involved in higher mental functions such as learning, remembering, thinking, and speaking

Cerebral Cortex - Speech

• Aphasia– impairment of language, usually caused by left hemisphere

damage either to Broca’s area (impairing speaking) or to Wernicke’s area (impairing understanding)

• Broca’s Area – an area of the frontal lobe that directs the muscle movements

involved in speech

• Wernicke’s Area – an area of the left temporal lobe involved in language

comprehension and expression

Specialization and Integration

Brain Activity when Hearing, Seeing & Speaking Words

Cortical Lateralization: Right and Left Hemispheres Function Differently

• Right hemisphere: superior to the left hemisphere in visual and spatial tasks, recognizing nonlinguistic sounds, identifying faces, and perceiving and expressing emotions

• Left hemisphere: superior to the right hemisphere at language, logic, and providing explanations for events

• Women may be more likely than men to use both hemispheres for language (their brains are more bilateralized).

Left-Handers are Different

• 65% have speech on the left (95 % RH)

• Weak correlations:

– + gifted & creative– - reading disabilities, epilepsy, alcoholism,

schizophrenia, allergies, MR

Brain Reorganization

• Corpus Callosum– large bundle of neural fibers connecting the

two brain hemispheres and carrying messages between the hemispheres

Brain Reorganization

Corpus Callosum

Brain Reorganization

– Split Brain– a condition in which the two hemispheres of

the brain are isolated by cutting the connecting fibers (mainly those of the corpus callosum) between them

Brain Reorganization

• The information highway from the eyes to the brain

Testing the Split Brain

The Brain Can Alter Its Neural Connections

– Plasticity: the flexibility of the brain to alter its neural connections following injury

– Hemispherectomy: a radical surgical procedure in which one of the cerebral hemispheres is removed to control life-threatening epileptic seizures. The remaining healthy hemisphere takes over many of the functions of the removed hemisphere.

– Plasticity is highest in childhood, but it also occurs in older adults.

Brain Reorganization

-- the brain’s capacity for modification as evident in brain reorganization following damage (functional plasticity) --and in experiments on the effects of

experience on brain development

Structural Plasticity)

Use it or Lose It

• 1. Avoid Harmful Substances

• 2. Exercise

• 3. Eat Sensibly

• 4. Challenge Yourself Mentally

• 5. Wear Your Helmet/Seat Belt.

Blood-Brain Barrier • A semipermeable wall of tiny blood vessels

that prevent certain chemicals in the bloodstream from reaching the brain

- Protects the brain from many “foreign substances” in the blood that may injure the brain,

- Protects the brain from hormones and neurotransmitters in the rest of the body, and

- Maintains a constant environment for the brain.

Blood-Brain Barrier

– Beneficial substances allowed to enter the brain through the blood-brain barrier are blood gases, such as oxygen, and small nutritional molecules.

– An important nutritional molecule transported out of the bloodstream in this way is glucose.

– Scientists have learned how to trick the blood-brain barrier into accepting therapeutic drugs through the bloodstream to the brain.

Blood-Brain BarrierBa