The Brain(10)

• The brain is responsible for all behaviors, thoughts, and experiences.
• This chapter covers basic neuroanatomy and neuroscience methods for studying the brain.

Learning Objectives:

• Name and describe the basic function of the brain stem, cerebellum, and cerebral hemispheres.
• Name and describe the basic function of the four cerebral lobes: occipital, temporal, parietal, and frontal cortex.
• Describe a split-brain patient and at least two important aspects of brain function that these patients reveal.
• Distinguish between gray and white matter of the cerebral hemispheres.
• Name and describe the most common approaches to studying the human brain.
• Distinguish among four neuroimaging methods: PET, fMRI, EEG, and DOI.
• Describe the difference between spatial and temporal resolution with regards to brain function.

The Brain's Limited Capacity

• Human cognition is limited; complex tasks cannot be performed simultaneously, suggesting shared resources.
• The brain uses oxygen and glucose delivered via blood, consuming 20% of our oxygen and calories despite being only 2% of our total weight.
• Cognitive limitations are more likely due to the way neurons communicate.
• Neurons can inhibit each other, limiting the amount of visual information the brain can respond to at one time.

The Anatomy of the Brain

• The brain can be divided into the brain stem, cerebellum, and cerebral hemispheres.

Brain Stem

• The brain stem is responsible for regulating respiration, heart rate, and digestion.
• Damage to the brain stem requires "life support".
• The brain stem includes the medulla, pons, midbrain, and diencephalon.
• It is involved in the sleep-wake cycle, sensory and motor function, and hormone regulation.

Cerebellum

• The cerebellum is critical for coordinated movement and posture.
• It also plays a role in cognitive abilities, including language.

Cerebral Hemispheres

• The cerebral hemispheres are responsible for cognitive abilities and consciousness.
• They consist of the cerebral cortex, white matter, and subcortical structures like the basal ganglia, amygdala, and hippocampus.
• The cerebral cortex consists of two hemispheres with folds (gyri) and grooves (sulci).
• The cerebral hemispheres are divided into the occipital, temporal, parietal, and frontal lobes.

Lobes of the brain

• The occipital lobe is responsible for vision.
• The temporal lobe is involved in auditory processing, memory, and multisensory integration.
• The parietal lobe houses the somatosensory cortex, handles visual attention, and multisensory convergence.
• The frontal lobe houses the motor cortex and structures for motor planning, language, judgment, and decision-making.
• The basal ganglia are critical to voluntary movement.
• The amygdala and hippocampal formation are part of the limbic system, which plays a role in emotion, aversion, and gratification.

A Brain Divided

• The two cerebral hemispheres are connected by the corpus callosum.
• Sensory and motor cortices operate contralaterally.
• Some functions are lateralized, residing primarily in one hemisphere.
• Severing the corpus callosum to create split-brain patients helps understand hemispheric function.
• Split-brain patients can simultaneously search visual fields and perform tasks like patting their head and rubbing their stomach.

Gray Versus White Matter

• Cerebral hemispheres contain both gray and white matter.
• Gray matter is composed of neuronal cell bodies and is responsible for metabolism and protein synthesis.
• White matter is composed of myelinated axons that conduct electrical signals.
• Both gray and white matter are critical for proper brain function.

Studying the Human Brain

• Knowledge about brain functions comes from various methods, with the strongest evidence being converging evidence from multiple studies.
• Phrenology, which attempted to correlate skull features with brain functions, was a popular early approach but has been proven wrong.

Neuroanatomy

• Dissection of brains (animals or cadavers) is a critical tool.
• Virtual dissection studies with CAT or MRI scanners are also conducted.

Changing the Brain

• Researchers induce lesions or ablate parts of the brain in animals, and infer function by measuring changes in behavior.
• Lesions of human brains are studied in patient populations only.
• Transcranial magnetic stimulation (TMS) uses brief magnetic pulses to induce electrical currents, interfering with normal neuronal communication.
• Transcranial direct current stimulation (tDCS) uses electrical current directly, potentially improving cognitive functions.

Neuroimaging Techniques

• Neuroimaging tools study the brain in action, with each having different spatial and temporal resolutions.
• Positron emission tomography (PET) records blood flow using a radioactive substance.
• Functional magnetic resonance imaging (fMRI) measures changes in oxygen levels in the blood.
• Electroencephalography (EEG) measures electrical activity and has greater temporal resolution but poorer spatial resolution.
• Diffuse optical imaging (DOI) can provide both high spatial and temporal resolution.