Chapter 2 : The Brain

Chapter 2 : The Brain

Neuroscience Research

• EEG : measures brain wave patterns and produces brain wave patterns of the cerebral cortex. Cannot measure inner layers of brain.

• PET : older neuroimaging procedure. Patients consume radioactive materials (similar to the dye used to detect kidney stones) so an X-ray machine can provide an electronic 3D representation of the patients brain. Primary measurement is by measuring blood and oxygen flow in the brain.

• fMRI : Does not need the exposure of radioactive materials to provide a measurement of blood and oxygen flow in the brain. The fMRI is more advanced because it provides video instead of static images of the brain.

The Building Blocks of the Brain

• When a certain area of the brain is being used, the fMRI will show large amounts of blood circulating the area. Blood leaves the area when certain tasks are stopped.

• Can you imagine asking an infant to sit still for 45 minutes in a tube? Not going to happen!

The Potential of a Nerve

• NIROT : alternate solution for infants where children wear an "optical nerve cap" that measures the absorption of infrared light by the brain. Unable to measure inner layers of the brain (cerebral cortex only).

• Neurons: individual nerve cells that carry sensory information (e.g., sight, sound, taste, touch) to the brain. The brain has around 75-100 million neurons (Azevedo et al., 2009)

• Like many computer processing theories; neurons are "workers", they perform the best when they work together. Neurons also tend to operate with pairs. They do not communicate randomly.

• Neuronal Mapping: As we gain more information, neurons are able to "link together" to create neural maps.

• The more neuronal mapping or connections a person has, the faster their brain processes information (i.e., a measure of intelligence).

• Neurons communicate with each other through chemicals. The process to start communication occurs electrically.

• Neurons have four basic parts: dendrites, soma, axons, and axon terminals.

• Glial Cells: cells that provide protection, energy, and communication to neurons. Higher amounts of glial cells may be correlated to I.Q. (e.g., Einstein), (Fields, 2004)

• Ions: very small electrically charged atoms that are inside and outside a neuron. Ions rely on electrical charges that are either positive or negative.

• Inactive neuron: there are more negatively charged ions inside the neuron and more positively charged ions outside the neuron.

• Active neuron: there are more positively charged ions inside the neuron and more negatively charged ions outside the neuron.

• Every neuron in your brain maintains an electrical charge of -70 millivolts. The analogy to a car battery is often helpful.

• Resting potential: even inactive neurons produce electrical charges. The electrical charge of an inactive neuron is referred to as the resting potential.

• Action threshold: the neuron is around -50 millivolts now and is becoming "alert" to signals from other neurons.

• Action potential/nerve impulse : the neuron has passed the action threshold and now sends messages to the nerve which relays the message to the axon.

• Given that we can respond in milliseconds automatically in some ways, researchers argue that nerve impulses travel up to 200 miles per hour (More et al., 2010).

Myelination

• Myelin: a fatty substance that coats some of the axons.

• Myelin Sheath: term used to describe an axon that is coated in myelin.

• The axons that are coated in myelin send messages faster than axons that are not coated in myelin.

• Saltatory Conduction : the term used to describe how myelinated axons delivery messages. Sometimes this process is simply referred to as myelination. This process tends to happen primarily until 25.

• Instead of sending messages down the axon, myelinated axons skip this step and send information over a gap (synapse) to the next neuron.

• Saltatory Conduction is responsible for helping us complete very fast reflexive behaviors (e.g., catching a fast ball or slamming on your brakes).

• Multiple Sclerosis: a disease that destroys the myelin in a person's body. This explains why people with this disorder often display slower response times, suffer from nerve pain, and eventually paralysis.

Anatomy of a Neuron

• Cell body: the large central structure of the neuron.

• Dendrites: the dendrites are responsible for delivering messages between connected neurons and the cell body. They are often described as "tree trunks" of the neuron due to their placement & function.

• Axon: a fiber at the end of the neuron which is responsible for sending messages to the brain and spinal cord. The longest axon is the sciatic nerve which is 3 feet long. We have around 3 million miles of axons connected to our brain (Fields, 2008).

• Axon Terminals: a way that axons, dendrites, and the Soma can be all connected to increase information processing speed. Think of "a bundle of nerves"

• Presynaptic Neuron: the neuron that sends the message.

• Postsynaptic Neuron: the neuron that receives the message.

• Terminal Button: the end of the dendrite where a chemical is released. This is the starting point in the process called neurotransmission.

• In recap, an electrical pulse (action potential) alerts the neuron to send a chemical (neurotransmitter) from the terminal button.

Neurotransmission

Neurotransmitters Continued

• Unsuccessful or malfunctioning transmissions of neurotransmitters is one explanation for most mental illnesses.

• Endorphins: neurotransmitters that block pain or create pleasurable feelings. A runner's high, pleasure during acupuncture, drug use, and having sex all produce endorphins (Boecker et al., 2008; Fuss et al., 2015).

• When people take morphine the body mistakes it for naturally produced endorphins (Pert & Synder, 1973).

• People who have problems with depression typically do not receive enough serotonin. Serotonin is a neurotransmitter responsible for calming the body, sleep, and appetite.

• Most drugs (illegal & pharmaceutical) mimic the effects of neurotransmitters. For instance, the brain responds to cocaine the same way it does dopamine. This is why so many drug overdoses are very similar to symptoms of mental illness (e.g., it is hard to diagnose a person high on crystal meth as not having schizophrenia).

• If drugs "exhaust" the production of neurotransmitters, the person has become tolerant to the chemicals. This means that the person would require more drugs or more neurotransmitters than normal.

• Neurons communicate with other neurons by chemical transmissions.

• Synapse: the very small gap between neurons. This is the gap that neurons "jump over". Less than a millionth of an inch wide (Myers & DeWall, 2018). Sometimes called synaptic cleft or synaptic gap.

• Neurotransmitter: neurons communicate via neurotransmitters. Neurotransmitters are chemicals released by a neuron that alters activity in other neurons and influence brain performance.

• Receptor Sites: Neuron A sends neurotransmitters to Neuron B. Neuron B receives these neurotransmitters through receptor sites. View receptor sites as gatekeepers for neurotransmitters. If closed, the neurotransmitter cannot effect the neuron.

• Inhibition/Protagonist: The neurotransmitter from Neuron A has alerted Neuron B to "calm down".

• Excitation/Antagonist: the neurotransmitter from Neuron A has alerted Neuron B to activate and become alert.

• Reuptake: the process by which the neurotransmitter is absorbed by the presynaptic neuron.

• Enzyme Degradation: the process by which enzymes break down the neurotransmitters.

The most common Neurotransmitters

• We have over 100 neurotransmitters in the brain.

• Given that we have so many, there are numerous neurotransmitters that we are unsure what their true purpose is.

• Some neurotransmitters are present in specific places only, so researchers typically start researching these chemicals first.

• An example is the hypothalamus. This area of the brain primarily receives the neurotransmitter dopamine.

• Acetylcholine (ACh): Motor control for muscles. We produce more of this as we age causing wrinkles and facial tissue to sag. Botox blocks the production of acetylcholine to reduce wrinkles. When our body cannot produce ACh, we tend to experience paralysis (e.g., Curare blow darts in South America).

• Anesthesia blocks the production of ACh and causes a person to be temporarily paralyzed.

• Epinephrine: neurotransmitter that creates an adrenaline rush. When a person's heart stops, doctors can use an EpiPen, which is a concentrated shot of epinephrine.

Brain Development

• The brain is the most developed organ in the body at birth

• Neurons are largely developed by birth, but they have not became specialized yet.

• When a neuron becomes connected to a neural fiber their specialized function is determined.

• In the first two years of life neural fibers and synapses are developing at a significant pace.

• Synaptic Pruning: the body makes an overabundance of neurons that never attach to neural fibers or make connections with synapses. These neurons do not receive stimulation and die out or move to other locations.

• The more stimulation a child is exposed to, the higher amount of synaptic connections occur (positive correlation). More synaptic connections typically means better brain functioning.

• Humans lose around 40% of their total neurons by the time they reach adulthood.

• An adult brain weighs around 3 pounds, 2% of our body weight. It consumes 20% of caloric energy (Myers & DeWall, 2018)

The Nervous System

Handedness and the Brain

• Around 5-10% of the global population is left-handed.

• Examples of outdated research associated with being left-handed: they are more artistic and creative, they are more likely to be a professional athlete, they live 7 years less than right handed people, left handed people are more likely to have anger issues.

• This is correlational research, that means the variables may be related (e.g., there might be a high % of successful left-handed athletes) but it does not mean one causes the other (e.g., being left-handed makes you a good athlete)

• Handedness is typically established in the womb. If the fetus sucks their left thumb in the womb, they are more likely to then be left handed.

• Position is also important. If the fetus is on their left side, the left hand is not free. Therefore, they are more likely to use their right hand (twin studies support this, why?)

• It is considered harmful to force a child to switch their writing hand without an important medical reason (e.g., stroke or amputation).

• Famous left-handed people: Bill Gates, Marilyn Monroe, Oprah Winfrey, Babe Ruth, Lady Gaga, Kurt Cobain, Jimi Hendrix, Paul McCartney, Justin Bieber, Gerald Ford, Ronald Reagan, George H.W. Bush, Bill Clinton, and Barack Obama.

• Most research argues that handedness is influenced more by biology than environment.

• In right-handed people, an area of the brain devoted to language and writing is in the left of the brain. For left-handed people, this part of the brain is either on the right side or split between the two.

Language and the Brain

• Broca's Area : a very small area in the frontal lobe of the brain. When this area of the brain is damaged or has a tumor, people are able to understand language but cannot accurately use words.

• Congresswoman Gabby Giffords was shot in the head years ago. The primary damage was in the Broca's Area. After over five years of therapy she has regained around half of her verbal language skills.

• Central Nervous System: the brain and spinal cord. For the most part, the brain is primarily in charge and the spinal cord relays messages.

• Peripheral Nervous System: nerve cells outside of the brain and spinal cord, usually in organs. The peripheral nervous system is a secondary nervous system responsible for transferring information to and from the Central Nervous System. The peripheral nervous system is further divided into the Somatic Nervous System and the Autonomic Nervous System.

• Nerves: bundles of neuron axons. You cannot see neurons, but can easily see nerves without a microscope. Nerves send messages from organs and muscles to the central nervous system (e.g., optic nerve). (Mason & Kandel, 1991)

• There are motor neurons, sensory neurons, and interneurons. We have billions of each type.

• Afferent Neurons: neurons that send information to the brain. Sensory neurons are an example. The optic nerve sends information to the brain for vision.

• Efferent Neurons: Neurons that receive information from the brain. To run you need motot neurons receiving messages from the brain.

• This video is medically graphic, put your head down and just listen if you do not feel comfortable watching!!!

Two Famous Case Studies of the Brain

P. Gage and his dramatic personality change

The University of Texas Sniper had an illness?

The Peripheral Nervous System

• Somatic Nervous System: focused on sensory information being received by sensory organs and the skeletal system. Responsible for voluntary movement.

• Autonomic Nervous System: focused on internal organs and glands. Primarily responsible for "self-governing" processes (e.g., breathing, digestion, blood flow, etc). The ANS is separated into the Sympathetic Branch and the Parasympathetic Branch.

• Sympathetic Branch: The alert system of the autonomic nervous system. This branch is activated when the brain is alerted to enter the "fight or flight" mode. Staying in this active mode too long kills animals in laboratory studies.

• Parasympathetic Branch: Alerts the body to relax and calm down. Occurs after the sympathetic branch has been activated. The parasympathetic branch is also responsible for making sure that people do not "max out" during alerted experiences (e.g., it makes sure blood pressure, respiration, and heart rate do not reach maximum levels).

Lateralization and Brain Plasticity

Parts of the Brain

• The brain is split into two hemispheres, four lobes, and three overall divisions.

• Lateralization: the process by which the two hemispheres have specialized functions.

• Believed to be a product of natural selection because it allows us to adapt to environmental pressures better. Allows a faster processing brain.

• Localization: different parts of the brain have different functions to perform. This makes our brain operate much faster than animals whose brains are not localized.

• Neuroplasticity: the infant brain is not lateralized yet and capable of change (i.e. highly plastic). This way the brain can adapt and other areas can take over if specific areas are damaged (Gutchless, 2014)

• Easier in children because the brain is still growing, but is possible in all age groups (e.g., physical therapy for 65 year old stroke victims).

• Dozens of studies have found evidence for experience-dependent brain growth (Draganski et al., 2004; Hänggi et al., 2010; Herholz & Zatorre, 2012). Examples include studying professional pianists, taxi cab drivers, and ballerinas. Their brain appears to be more specialized in areas related to their profession (Bavelier et al., 2000; Pantev et al., 1998).

• People who are born blind often use the visual part of the brain to have a stronger ability to locate distance based on hearing (echolocation?) (Thaler et al., 2011,2014)

The Hindbrain

Development of Cerebral Cortex

The Forebrain

• There is the left and right hemisphere of the brain.

Lobes of the Cerebral Cortex

How Do We Know This About The Brain?

• Occipital Lobe: located in the back of the brain. This lobe is mainly responsible for vision. It is broken down into smaller areas of visual specialization (e.g., depth vs peripheral)

• Wilder Penfield: one of the first neurosurgeons. He primarily worked with epileptic patients.

• The four lobes of the brain are the occipital, parietal, temporal, and frontal lobe.

• Examples of different visual aspects the brain processes: colors, shapes, motion, depth, and patterns.

• Penfield mapping: Penfield electrically stimulated the brain of epileptic patients and asked them "where do you feel this?". The patients would report the location and Penfield "mapped" the somatosensory cortex.

• Parietal lobe: is responsible for touch, movement, and is famously known for the primary somatosensory cortex.

• Finally, the three main divisions are the hindbrain, midbrain, and forebrain.

• Hemineglect: stroke victims will sometimes have permanent damage to the right parietal lobe. This causes them to lose all awareness of the left side of their face.

• The parietal lobe is split by the corpus callosum and is separated by left/right sides.

• Cerebrum: the left and right hemisphere of our brain. 85% of the brain's total mass.

• Cerebral Cortex: outer layer of the cerebrum. Has around 20-23 million neurons and synapses (de Courten-Myers, 2005).

• The cerebral cortex takes longer to fully develop than any other part of the brain. The frontal lobe takes the longest to develop and does not fully mature until late 20s.

• Corpus Callosum: the strip of tissue that connects the two hemispheres of the brain. Responsible for sending information between the two sides.

• The left hemisphere controls the right side of the body, the right hemisphere controls the left side of the body.

• The hindbrain and midbrain encourage reflexive behaviors for survival. The cerebral cortex allows advanced, critical thinking such as planning and culture.

• The right side of the brain receives touch information from the left side of the body. The left side of the brain receives touch information from the right side of the body.

• Unique to humans and primates. Evolutionary theorists believe this is the newest part of the human brain.

• The forebrain is separated into the cerebral cortex and the subcortical regions. The five subcortical regions are: the thalamus, hypothalamus, hippocampus, amygdala, and the basal ganglia.

• Thalamus: receives sensory information and encodes the message for the brain. It does NOT delivery olfactory messages. During sleep the thalamus makes sure we are not alerted by unimportant sensory information.

• Reticular Formation: delivers messages from the thalamus to other areas. Helps with multi-tasking. When your reticular formation is removed, you typically enter a coma (Moruzzi & Magoun, 1949).

• Basal Ganglia: largely responsible for planning, reward, and motivation.

• Temporal Lobe: Area of the brain responsible for hearing and facial recognition. On the side of the brain.

• The hindbrain: the base of the brain that connects directly to the spinal cord (called brainstem). Almost all mammals have a hindbrain.

• The hindbrain is sometimes called the "primitive brain" because evolutionary theorists argue this was the starting point in all brain development.

• We separate the hindbrain into three major parts: the medulla, pons, and cerebellum.

• Medulla: responsible for automatic survival functions such as breathing, heart rate, swallowing, vomiting, urination, and orgasm. If a person receives enough damage to the medulla death can be immediate.

• Pons: responsible for sleeping, arousal (safety & sexual), and coordination between left and right sides of the body.

• Cerebellum: Latin for "Little Brain". It is responsible for motor function, understanding time, and pick out specific sounds and textures.

• Damage to different parts of the cerebellum cause different outcomes. Damaging the top of the cerebellum results in people unable to tilt their head. Damage to the bottom makes a person lose their sense of balance. Finally, damage to the sides results in loss of limb control.

• Primary Somatosensory Cortex: a region of the parietal lobe that helps us determine where we are experiencing touch on our body.

• Spinal Cord: a "rope" of nerves that stretches from above our pelvis to the base of our skull. The primary function of the spinal cord is to deliver messages from the body to the brain.

• Severe damage to the temporal lobe can cause hearing loss.

• For example, one small part of the brain is responsible for detecting touch on our tongue. This means we "feel" with our brain instead of actual body parts.

• Prosopagnosia: damage to the temporal lobe can cause people to lose the ability to recognize faces. ALL FACES WILL APPEAR BLURRY.

• Primary Motor Cortex: area of the parietal lobe that helps us acknowledge we are moving our body.

• It seems that the temporal lobe may also be associated with visual memory recognition.

• Gray Matter: tissue in the spinal cord that does NOT have myelin. These neuronal messages usually stay in the spinal cord.

• Somatosensory Homunculus: A human depiction of how much space of our brain is actually devoted to particular senses.

• Fusiform Facial Area: part of the temporal lobe that always activates when looking at a person's face (in real life OR pictures)

The Limbic System

• White Matter: tissue in the spinal cord that is myelinated. This tissue is able to send messages to the spinal cord AND brain.

• Limbic is greek for "border". It borders the hindbrain and cerebral hemispheres.

• Hippocampus: primarily related to memory. It's specialties are visuospatial information.

• Amygdala: Largely responsible with emotions. It determines appropriate emotional responses. It is also responsible for understanding facial expressions, fear, and sexual arousal.

• When aggressive monkeys have their amygdala removed they usually become docile (Berntson et al., 2011).

• Animals and humans that have amygdala damage become less afraid of strangers (Harrison et al., 2015).

• Hypothalamus: Hypo = below. It means "below the thalamus". Similar to the functions of the hindbrain in that it regulates automatic functions. It is responsible for body temperature, sleep, blood pressure, and basic needs for survival (hunger, thirst, and sex).

• Nucleus accumbens: reward center of the brain. Located in the hypothalamus. Active when we perform pleasurable actions (Hamid et al., 2016).

• The brain also contains both white and gray matter.

The Mammal Brain

• Mammals have the most developed brain of any organism.

• Larger brains usually means they are more intelligent animals (usually). Examples include primates, whales, elephants, octopuses, and dolphins.

• The larger the brain, an animal is more likely to have a frontal cortex. Very few animals have this area of the brain.

• Animals with smooth brains are less capable of multitasking. Research theorizes that wrinkled brains are an evolved response.

• The grooves (sulci) and wrinkles (gyri) in the brain make it where a larger brain can fit in a smaller skull.