(Week 1) The Brain and Behavior

[Music] biological basis of behavior the brain is where every introductory psychology course begins and it's also among the first chapters covered by introductory textbooks we start here because psychologists are interested in understanding behavior emotions thoughts and consciousness all of which originate in the brain in the past three decades the study of the brain's role in behavior known as behavioral neuroscience or biological psychology has expanded exponentially and many new vibrant areas of research have emerged that study behavior anywhere from molecular interactions inside of the individual nerve cells to broad and expansive efforts to understand how large networks of nerve cells give rise to emotions and other experiences of consciousness as is now widely known the brain is a massive network composed of billions of brain cells wired together to pass information back and forth this system is actually a complex triad of architectural electrical and chemical components working in concert in this video we will describe each component and begin to think about potential projects that will help further develop your understanding of the relationship between the brain and both conscious experiences and behaviors working to understand something so incredibly complex necessarily requires some amount of oversimplification at every level what's important to remember as parts of the brain are labeled and processes within the brain are defined is that emergence is always at play in science emergence occurs when the whole is greater than the sum of its parts meaning the whole has properties its parts do not have a cell for example is just a group of chemicals none of which are alive but through complex interactions of those lifeless chemicals life emerges as is also true of a brain mind relationship not a single one of a hundred billion cells that make up your brain is conscious and yet through the complex exchanges of chemical and electrical signals within the vast network these cells create consciousness emerges architecture to begin describing the specialized regions of the brain involved in various behaviors will begin with the hind brain which controls the most basic functions of life first there's the medulla the region of the brain that adjoins the spinal cord the medulla controls for breathing heart rate blood circulation and balance above the medulla is the pons the pons controls attentiveness and the timing of sleep and dreaming damage to certain parts of the pons can put a person into a semi-permanent sleep like state additionally REM sleep may also originated in the pons inside the ponds in the medulla lies portions of the reticular formation a network of nerves extending from the spinal cord right up through the thalamus the reticular formation plays a role in autonomic functions of the body like circulation respiration and digestion but also in pain modulation sleep and consciousness sitting on top of the pons is the midbrain this structure helps orient an organism in the environment and guide movement toward or away from stimuli the midbrain is also believed to help regulate our experience of pain modulate mood and shape motivation just behind the pons and medulla is the cerebellum the cerebellum coordinates voluntary movements such as posture balance and coordination resulting in smooth and balanced muscular activity damage to this organ can cause problems in spatial reasoning discriminating sounds and integrating input received from various sensory systems more recent evidence suggests that the cerebellum may also help as judge time modulate our emotions and even discriminate sounds and textures you next the forebrain is made up of brain structures including the thalamus hypothalamus amygdala hippocampus and cerebral cortex the thalamus is involved in sleep wakefulness and in relay motor and sensory signals to the cortex the thalamus also closes pathways of incoming sensations during sleep the hypothalamus is positioned underneath the thalamus it has been found to be involved in controlling motivated behaviors such as eating drinking and sexual activity as well as involuntary rhythms such as the sleep/wake cycle and detecting when the body is too cold or too hot the amygdala is believed to play a role in emotional response specifically anger and it is involved in determining whether a stimulus is a threat or not it helps predict when something frightening is about to happen they make the Liz particularly active for instance when playing video games are seeing fearful faces [Music] nearby the hippocampus plays an important role in learning memory spatial orientation and creating new memories of all these varied and crucial roles that these many brain regions play it's the cerebral cortex that receives the most careful consideration and study among behavioral neuroscientists in fact the cortex is involved in every thought and perception as well as our ability to produce an understand language and to construct and experience emotion it is crucial in order to believe organize remember and even to hope structurally the cortex is a thin covering on the outer surface of the brain on average just three millimeters thick still the cortex makes up approximately 80% of the human brain this enormous volume is made possible by the fact that the cortex consists of a very large sheet of tissue crumpled up into the limited space inside the skull this crumpling produces the brain's most obvious visual feature there wrinkles some of the wrinkles are actually deep grooves that divide the brain into different anatomical sections the deepest groove is the longitudinal fissure dividing the brain into two halves the left and the right cerebral hemispheres which are connected through a thick band of fibers called the corpus callosum the corpus callosum allows communication between the two hemispheres of the brain it is responsible for transmitting neural messages between both the right and left hemispheres [Music] the right hemisphere controls muscles on the left side of the body and the left hemisphere controls muscles on the right side of the body this is also true of sensory information sensory information from the left side of the body crosses the corpus callosum for processing in the right hemisphere while information from the right side of the body crosses to the left hemisphere for processing therefore damage to one side of the brain will affect the opposite side of the body other fissures divide the cortex in each hemisphere into four lobes rather like continents in the brain the frontal lobes form the front of the brain right behind the forehead the central fissure divides the frontal lobes on each side of the brain from the parietal lobes the brain's topmost part the bottom edge of the frontal lobes is marked by the lateral fissure and below this are the temporal lobes finally at the very back of the brain directly adjoining the parietal and temporal lobes are the occipital lobes many researchers divide cortical tissue into three broad types located within each of these lobes sensory areas receive and interpret information from the eyes ears and other sense organs and the motor areas control our behaviors each of the remaining areas are typically called association areas and are said to be involved in many complex processes including those broadly referred to as thinking the primary motor cortex is located in the back of the frontal lobe and stimulating different parts of this area leads to movement of specific body parts that is each portion of the primary motor cortex corresponds to a specific part of the human body this map is often summarized with a motor homunculus which is a picture showing each body part next to the bit of motor projection area that controls its movement with equal sized areas of the body failing to be controlled by equal amounts of cortical space instead the parts that we can move with the greatest precision for example the fingers the tongue receive more cortical area than those which we have less control the shoulder the abdomen the primary somatosensory cortex is directly behind the primary motor cortex in the front of the parietal lobe this area is the initial receiving area for sensory information arriving from the skin senses as with the motor cortex space in the somatosensory area is proportional to the sensitivity of the body region with much more space for lips and fingers for example than for larger but less sensitive areas of the body the brain has similar primary cortical areas for vision and for hearing and these are located in the occipital and temporal lobes respectively notably the prefrontal cortex has received some of the most intense attention from neuroscientists because of its involvement in planning decision-making mood personality and self-awareness despite ample evidence of seeming specialization within brain regions it's important to remember that complex mental functions don't reside in any one place in the brain complex processes like memory language and attention result from synchronized activity from many brain areas the achievements we can easily observe thinking feeling or acting require exquisite coordination among brain regions and at the root of this coordination lie the neurons that is the communication cells contained within the brain and spinal cord there are around 10 to 15 times as many neurons in the brain as there are people on earth and each of the more than 85 billion neurons receive process and transmit messages to thousands of other neurons with an estimated hundred sixty trillion neural connections in the human brain the functioning of our brain depends on continual crosstalk within complex networks or work groups of neurons the neurons specializes in sending and receiving information a description of a neuron typically includes the dendrites the cell body and the axon the dendrites the input side of the neuron receives signals from many other neurons in most neurons the dendrites are heavily branched the cell body contains the neurons nucleus and all the elements needed for normal metabolic activities of these cells the axon finally is the output side of the neuron and sends neural impulses to other neurons the axon usually extends outward from the cell body and it may fork into several branches at its end neurons come in many shapes and sizes their cell bodies vary from five to about a hundred microns in diameter in comparison the average human hair has a diameter of about a hundred microns neurons dendrites are typically pretty short say a few hundred microns axons however can be much longer for example the longest axons and humans are those of the motor neurons which transmit neural impulses from the brain to the muscles as a result these particular neurons with their small cell bodies connected to very long axons have roughly the same proportions as a basketball all attached to an electrical cord a mile and a half long the brain also contains another type of cell called glia whose function is just beginning to be understood for many years scholars thought glia only played a few roles holding the neurons in place and supplying them with nutrients and oxygen turns out however that glia cells have a rather broad set of vital functions first glia do provide nourishment for the neurons but also play a role in controlling the nutrient supply for example the sugar glucose is the main fuel for the nervous system but most of the energy that neurons need does not come from glucose directly instead the glia convert glucose into another molecule called lactate that feeds the neurons the glia cells are also sensitive to the activity level in each neuron and increase the blood flow providing more oxygen and fuel whenever the neurons in the brain region become more active additionally glia cells are involved in the brains development before birth and in the months afterwards the human brain grows at a remarkable rate as its cells rapidly reproduce and differentiate the newly created neurons then migrate from one position in the brain to another moving at a speed of up to one millimeter each day this migration is guided by glia cells acting as guide wires then once the neurons have reached their destinations and established the appropriate connections the glia produce chemicals that help shut down the process of neural growth in this way the glia ensures a relatively stable pattern of connections the glia may also have other jobs to do for example several recent studies suggest that glia can talk back to neurons sending signals that help regulate the strength of connections between adjacent neurons in some circumstances glia can also release chemicals that increase the reactivity of neurons the neuron is in some ways just a cell it has a nucleus and a cell membrane that defines boundary what makes a neuron distinctive though is its sensitivity to stimulation when stimulated a cascade of changes are produced that results in an electrical signal called an action potential this signal sent from one end of the neuron to the other is the neurons main response to input as well as the fundamental information carrier of the nervous system when a neuron is at rest there is an uneven distribution of ions across the cell membrane when a neuron is sufficiently stimulated an action potential is generated and travels along the axon to the terminal branches by means of a change in polarity across the membrane of the axon in response to a signal from another neuron positively charged sodium and potassium gated ion channels open and close the positively charged sodium ion channels open at the beginning of the action potential and positively charged sodium ions move into the axon causing depolarization repolarization occurs when the positively charged potassium channels open and the positively charged potassium ions move out of the axon creating a change in polarity between the outside of the cell and the inside in other words during an action potential positively charged ions flow rapidly into the neuron and then just as rapidly flow out this electrical impulse travels down the axon in one direction only to the axon terminal where it signals other neurons when an action potential occurs we can describe it as the neuron firing although the flow of ions in or out of the neuron is fast even so the full movement of the action potential across the neuron is surprisingly slow in that it travels at about one meter per second if this were the top speed for neural signals it would be a serious problem for most organisms because most fast paced actions would be impossible fortunately yet another function of glial cells is to increase the speed of neuronal communication the glia that accomplished this are mostly made of a fatty substance known as myelin soon after birth these glia cells start to wrap themselves around the axons of neurons especially the longer axons that span greater distances and required greater transmission speed this myelin sheath covers a portion of the axon and soon the entire length of the axon is covered by a series of these wrappers crucially though there are gaps called the nodes of ranvier between the successive wrappers and it's this combination of wrappers and gaps that speeds up the nerve impulses traveling along these myelinated axons if an axon is myelinated ions can move into or out of the axon only at the nodes of ranvier at all other locations the axon is enclosed within its myelin and this blocks ion flow therefore in essence the action potential has to skip from node to node and thanks to these jumps it more quickly at speeds up to a hundred twenty meters per second it is also important to mention that the neuron either fires or it doesn't there's no in-between though we need some way to differentiate the weak signals from the strong this is partially accomplished by more intense stimuli exciting a greater number of neurons this happens because neurons vary tremendously in their excitation thresholds as a result a weak stimulus stimulates only neurons with relatively low thresholds while a strong stimulus stimulates all of those neurons plus others whose threshold is higher the chemical messages when the action potential reaches the axon terminal it triggers the release of chemicals known as neurotransmitters into the synaptic cleft which is a fluid-filled gap between neurons that's less than a millionth of an inch wide neurotransmitters from this presynaptic neuron are taken up that is bind to specific receptor sites on dendrites of nearby neurons stimulating them and starting their action potential so what happens to the neurotransmitters after they've affected the postsynaptic neuron they can't just stay where they are because they might continue exerting their effects long after the presynaptic neuron has stopped firing to avoid this problem some neurotransmitters are deactivated by special cleanup enzymes that break them up into their chemical components more commonly though neurotransmitters are not destroyed but they're reused in this process called synaptic reuptake the neurotransmitter molecules after they've had their effect on the postsynaptic cell are rejected from the receptors vacuumed up by the molecular pumps back into the presynaptic axon terminals and repackaged for future use through this process one individual neuron influences thousands of others and thousands of neurons can influence one all simultaneously this is the brain in action in any given moment our brain is working to generate just the right balance of neurotransmitters at night for example the brain needs to increase rest and recuperation neurotransmitters level to transmit certain thoughts in a calming tranquil and relaxing way to induce sleep examples of these neurotransmitters are melatonin and serotonin in the morning the brain must lower its rest and recuperation neurotransmitter levels and increase its excitatory neurotransmitter levels for us to function consciously examples of excitatory neurotransmitters are acetylcholine glutamate aspartate noradrenaline and histamine in stressful situations it must increase levels of fight-or-flight transmitters for example epinephrine and norepinephrine that help you to remain calm and in control it's critical that all of the major neurotransmitters are present in sufficient amounts all the time when there are insufficient amounts of neurotransmitters it upsets the chemical balance of our brain hence some symptoms may be experienced including depression lethargy helplessness mood swinging anxiety panic irritability insomnia and aggression importantly neurotransmitters can be classified by function excitatory neurotransmitters these types of neurotransmitters have excitatory effects on a neuron they increase the likelihood that the neuron will fire an action potential some of the major excitatory neurotransmitters include epinephrine and norepinephrine inhibitory neurotransmitters these types of cells have an inhibitory effect on the neuron they decrease the likelihood that the neuron will fire an action potential some of the major inhibitory neurotransmitters include serotonin and gaba now some neurotransmitters such as acetylcholine and dopamine can have both excitatory and inhibitory effects depending on the type of receptors that are present glutamate and GABA are the most common neurotransmitters in the central nervous system neurons in virtually every brain area use these two chemical messengers to communicate with each other glutamate rapidly excites neurons increasing the odds that they will talk with other neurons the release of glutamate is associated with enhanced learning and memory when abnormally elevated glutamate may contribute to schizophrenia and other mental disorders because in high doses it can be toxic damaging neural receptors by over stimulating them gaba in contrast inhibits neurons by dampening neural activity that's why most anti-anxiety medications bind to gaba receptors they tend to suppress overactive brain areas linked to worry gab is considered an absolute workhorse in our central nervous system playing critical roles in learning memory and sleep beyond an excitatory or inhibitory effect there are also various ways to enhance our impede the actions of a neurotransmitter by introducing chemicals in the form of medications chemicals that enhance a transmitters activity are called agonists those that diminish a transmitters activity are called antagonists agonist exert their influence in many ways some agonists actually mimic the neurotransmitter so on their own they can activate the receptors other agonists block the reuptake of the transmitter into the presynaptic cell and still others work by counteracting the cleanup enzyme that breaks down the transmitter after this triggered a response both of these mechanisms have the effect of leaving more transmitters within the synaptic gap this increases the transmitters opportunity to influence the postsynaptic membrane and so ends up increasing both the strength and the duration of the transmitters effect antagonists work through similar mechanisms but with the opposite effect thus some antagonists prevent the transmitter from working by binding themselves to the synaptic receptor and blocking off the transmitter essentially serving as a kind of putty in the synaptic lock other antagonists operate by speeding up reuptake and others by augmenting clean up enzymes cocaine for example is an agonist it works by blocking the reuptake of dopamine norepinephrine and epinephrine into the presynaptic molecules the effect is aroused throughout the body restlessness and in some cases euphoria many antidepressant medications including prozac Zoloft and paxil work in roughly the same way but specifically block the reuptake of serotonin still other drugs are antagonists some of the medications used for schizophrenia for example block postsynaptic receptors and seem effective in helping patients control psychotic thinking and restore a normal functioning in their lives opiates such as codeine and morphine also function as agonists increasing receptor site activity they reduce our emotional response to painful stimuli by binding with opioid receptors and mimicking endorphins tranquilizers such as xanax whose generic name is alprazolam diminish anxiety by stimulating GABA receptor sites thereby driving down neural activity another key idea is that individual neurons are selective in what neurotransmitter they will respond to many neurons are responsive to more than one neurotransmitter but even so each neuron has its own pattern of sensitivities for example a neuron inhibited by gaba will respond differently or perhaps not at all two molecules of serotonin that happened to float by this notion of receptors being selective in their response and the idea of different neurotransmitters providing different signals are key elements in controlling the complex flow of information throughout the brain though the neurotransmitter system has provided some evidence specificity at the molecular level it's important to remember that a mental event thought perception memory or emotion is not created by only one set of neurons or one type of neurotransmitter instead combinations of different neurons and associated neurotransmitters can create similar instances of these experiences neuroscientists call this principle degeneracy degeneracy means many to one many combinations of neurons can produce the same outcome in the quest to map the brain degeneracy is an important humbling reality check to be humbled even further the opposite is also true about the brain along with the generous II many parts of the brain serve more than one purpose the brain contains core systems or networks of neurons that participate in creating a wide variety of mental states a single core system or network can play a role in thinking remembering decision-making seeing hearing and experiencing a core system is one too many that is a single brain area or network contributes to many different mental states and behaviors so from this brief description of the structure and function of the brain it is clear that neuroscientists have made enormous progress but there are also many many miles to go within the field of psychology we have the opportunity to learn about many other perspectives and types of analysis that help us to understand our behaviors and mental states schwartz and colleagues in their recent article in american psychologist actually warned against what they call neuro seduction a tendency to accept dubious claims when couched in terms of neuroscience and one study undergraduates judged logically flawed reports of research findings to be more convincing when the phrase brain scans show was used likewise a company Lumosity seduced more than seventy million subscribers with its brain training games that were supposedly based on neuroscience that is until the Federal Trade Commission found the company guilty of false advertising and slapped it with a hefty fine even if claims about the brain and its role in behavior have evidence to back them it's not unusual that they represent and as yet still necessary oversimplification of the vast complexity that our brains actually hold [Music]