Brain Anatomy. Science erases what was previously true. Disclosure 9/16/2016

Transcription

1 Brain Anatomy David Mays, MD, PhD Disclosure Dr. Mays is not on any drug advisory boards, paid for doing drug research, or otherwise employed, funded, or consciously influenced by the pharmaceutical industry or any other corporate entity. No off label uses of medications will be discussed unless mentioned in the handout and by the presenter. No funny business. Science erases what was previously true. John McPhee 1

2 How Does This Happen? The brain is the most complex structure we know of in the universe. The brain takes various inputs some we call sight, some skin sensation, some sound, some smell, some taste and creates an internal model of the outside world. Making this model is a creative act of the brain. The brain does not just take a picture of the world. The Bottom Line The brain is a 5 pound mass of biological tissue, operating inside a closed, dark space, that takes electrical and chemical signals from outside of us and associates them together to create an internal model of the world. This internal model is not a picture of the world, but an approximation of the world. The Bottom Line Millions of years of evolution have allowed our genes to pre wire certain circuits to make it more likely we will survive: desire to eat, aversion to harm, caring for young, instinct for bonding, sensitivity to language, etc. But in humans, instincts share influence with the ability to learn new behaviors. Hence our long period of dependency. 2

3 The Bottom Line The brain never quits growing and changing in response to experience. Brain Anatomy and Function The anatomy of the human brain is extremely complex and would generally requires a full semester of intense study. You don t want to do this. Trust me. Today, instead, we will hit the highlights covering basic anatomy and some of the most recent interesting findings about function. Vocabulary Saggital: the vertical plane that divides right and left Coronal: vertical plane that divides into front and back Axial: horizontal plane that divides top and bottom Dorsal: near the back or upper surface Frontal: toward the front Ventral: lower toward the front 3

4 Basic Neurological Tests Gait: Can you walk into the room? Speech: Can you talk and understand questions? Intellectual functions: Can you carry on a conversation about your history? Can you do a little math? Brain Anatomy The human brain weighs about 3 pounds and uses 20% of the energy of our body (but very efficiently about 11 watts.) It never rests. The sleeping brain is as active as the conscious brain. We just don t know what its doing. The human brain is over 3x as large as a typical mammal with an equivalent body size. Most of the difference is the cerebral cortex, a layer of nerve cells over the cerebrum. Especially expanded are the frontal lobes. The portion devoted to vision is also expanded. Brain Anatomy The brain is protected by the thick bones of the skull, a thick membrane (meninges), cerebrospinal fluid, and isolated from the bloodstream by the blood brain barrier. The consistency of the brain is similar to soft gelatin. The brain is estimated to contain 80 90,000,000,000 glial cells and 80 90,000,000,000 neurons. There are 1,000,000,000,000,000 synaptic connections. The purpose of these cells is communication. 4

5 Brain Anatomy The brain consists of 3 main parts The brainstem The cerbellum The cerebrum Brainstem The brainstem lies underneath the cerebrum and resembles a stalk to which the cerebrum is attached. The brainstem includes the midbrain, pons, and medulla, connecting to the spinal cord. It performs many autonomic functions such as breathing, heart rate, body temperature, wake and sleep cycles, digestion, sneezing, coughing, vomiting, and swallowing. Cerebellum The cerebellum lies underneath the cerebrum and behind the brainstem. The cerebellum coordinates muscle movements, maintains posture and balance. It is involved with the physical coordination of previously learned activities riding a bike, brushing your teeth. It may also support higher learning activities math, music, language, advanced social skills, but this is not well understood. The cerebellum keeps growing well into the 20 s. 5

6 Cerebrum The cerebrum is divided into two hemispheres right and left which are joined by a bundle of fibers called the corpus callosum. Each hemisphere controls the opposite side of the body. The left hemisphere specializes in speech, comprehension, arithmetic, writing. It is fanatic about organizing and categorizing. The right hemisphere specializes in artistic and spatial ability, creativity, musical skills. It sees the world as preorganized sensations. 8% of people are left handed and may have language skills in the right hemisphere (33%). Seeing Patterns is the Default Mode We cannot stop ourselves from seeing patterns in the world. Split brain experiments and other tests have shown that we normally create a story for everything that happens, often unconsciously. We want to believe the world is less random than it is. Which sentence do you prefer?: The king died and then the queen died. The king died and then the queen died of grief. Dopamine High levels of dopamine appear to lower skepticism and make people more vulnerable to pattern detection. Treatment of Parkinson s Disease with L dopa, for instance, can lead patients to be more superstitious, more interested in astrology and gambling, etc. Dopamine dysfunction is also linked to paranoia seeing patterns in events when other people do not. 6

7 The Narrative As mental health professionals, we should be aware of the nature of the human brain to be drawn to the simplest, most compelling narrative and understand that the story is not necessarily the truth. Cerebral Cortex The cerebrum consists of an outside layer (cortex), an underlying collection of neurons and their connecting axons, and primitive deep brain structures at the core. There are also several chambers that produce and hold cerebral spinal fluid (ventricles.) Deep Brain Structures Thalamus: relay station for almost all information coming to the cortex. Important for pain, attention, alertness Hypothalamus: master control of the autonomic nervous system: arousal level, noxious events, hunger, thirst, sleep, sexual response, body temperature, blood pressure, emotions, and hormone secretion. Links nervous system to the endocrine response to stress. Will prime the amygdala to consolidate fearful memories. 7

8 Deep Brain Structures Pituitary gland: the master gland sexual development, bone and muscle growth, stress reactions, immune system Pineal gland: body s internal clock circadian rhythms, melatonin Deep Brain Structures Habenula: The habenula is activated by unexpected negative events, like a punishment out of the blue, or the absence of an expected reward. It is part of the disappointment circuit. It lacks an opposing set of neuronal inputs. Antidepressants are active here, and may correct the negative bias present in depression. Deep Brain Structures Basal ganglia: movement coordination with cerebellum to control fine and large motor movements. Secretary to the prefrontal cortex. It is tightly connected to the prefrontal cortex. Parkinson s disease results from lack of dopamine here. With the insula, the center of the emotion of disgust physical and moral. The caudate is the seat of fast automatic, unconscious operations. 8

9 Deep Brain Structures Nucleus accumbens: part of the basal ganglia, a reward center associated with drug intoxication. It places a value on stimuli. Limbic system: cingulate gyri, hypothalamus, amygdala, hippocampus emotions, learning, memory Amygdala The amygdala receives input from the thalamus about body states (stress, alarm) and responds to emotional input and memories. It mediates arousal, directs motivation. It enhances learning and memory for emotional events. This includes recognizing when others are afraid. The amygdala processes most emotional information in teens. (Adults rely more on the prefrontal cortex to understand and evaluate fear.) Amygdala The amygdala is best known for fear responses, but it also responds to positive stimuli. It is an important component of directing attention to emotionally salient events. Its neurons respond to sight, sound and touch. Damage here reduces signs of anxiety and impairs decision making. (Animals won t learn to avoid foods that make them sick.) 9

10 Amygdala and Callousness Individuals with high callous and unemotional traits generally show reduced amygdala activation. Amygdala hypo responsivity may correspond to callousness, and may be a hallmark of the psychopath. A hypo responsive amygdala creates difficulty in recognizing fear shown by others. Cerebral Cortex The cerebral cortex is so large it overshadows every other part of the brain. This is where consciousness resides. Extensive damage here will produce a permanent coma. The cortex is a sheet of neural tissue, folded to fit inside the skull. (A groove is called a sulcus and a ridge is called a gyrus.) Each hemisphere has a total cortical surface area of 1.3 square feet. Cerebral Cortex The cerebral cortex contains about 70% of the brain s nerve cells, although it is only a quarter inch thick. The high concentration of nerve cell bodies gives the cortex a darker color than the rest of the brain gray matter. Underneath the cortex, the brain is full of connecting fibers of neurons (axons) that are largely covered in myelin (fat insulation) white matter. 10

11 Cerebral Cortex: Lobes There are five lobes of the cerebral cortex, 4 named after the bones that overlie them. Frontal lobe: speaking/writing (Broca s area), personality, judgment, body movement, concentration, inhibition Parietal lobe: touch, spatial/visual perception Occipital lobe: vision Temporal lobe: understanding language (Wernicke s area), memory, hearing, sequence organizing Insula, or insula cortex, underneath the parietal lobe: integration of sensation and emotion Anterior Cingulate The anterior cingulate is a neural alarm system that signals when something is wrong or when an autonomic process should get conscious attention. It is particularly active during physical and social pain, probably carrying the emotional component. It also fires when others experience pain (empathy), working in tandem with the insula. Hyper responsiveness here is a marker for developing PTSD. It monitors for conflicts and errors. It helps us distinguish between conflicting perceptions: My parents loved me. My parents hurt me. Anterior Cingulate The anterior cingulate is actively involved in problem solving and moral dilemmas, integrating with emotional and sensory data, with strong connections to the dorsolateral prefrontal cortex. The anterior cingulate is also involved with behavioral motivation. Dysfunction results in amotivation and apathy. 11

12 The Ventral Cingulate The ventral cingulate appears to regulate emotional conflict by damping the amygdala. Disorders in these circuits are found in both anxiety and depression. The Frontal Cortex The frontal/prefrontal cortex evolved from the motor cortex and is the most complex part of the brain. It is does not fully mature for at least 25 years. The frontal lobe is the last to develop and the first to degrade. There are three major divisions: medial frontal, orbital frontal, and dorsolateral. Medial Frontal Cortex Includes the anterior cingulate (emotional and social thinking). Integrates information in support of complex goals and aspirations. Becomes more active when jazz musicians improvise. May, in part, be the center of the personal, the self. This is the area damaged in Phineas Gage. 12

13 Ventromedial Prefrontal Cortex The vmpfc is involved in decision making, integrating information from the amygdala. It is highly involved in moral decision making, utilizing emotional input. People with damage to the vmpfc generally use utilitarian strategies in solving highly emotionally evocative moral dilemmas (Do I save my child or 3 strangers?) Orbitofrontal Cortex The orbitofrontal cortex is very closely associated with the limbic system. It is highly involved with emotion, mood, drives, and rewards. It is a key area in integrating emotions into decision making. But it also regulates emotion, controls moods, and is involved in decisionmaking tasks. It receives a lot of sensory input. It can evaluate behavioral responses to the environment. Animals without a prefrontal cortex lose the ability to extinguish fearful memories that are no longer relevant. Orbitofrontal Cortex The right hemisphere is apparently involved in mediating the rules of social convention. Damage here is likely to result in aberrant social behavior poor social judgment, impulsive decisions, decreased empathy (pseudo psychopathic disorders). One hypothesis of the etiology of psychopathy is that a hypoactive amygdala may fail to trigger a strong enough response in the orbitofrontal cortex to enhance emotional learning and memory. 13

14 Dorsolateral Prefrontal Cortex Coldly calculating. Involved in executive functioning, organizing behavior, solving complex problems, shifting strategies even when there is strong emotional investment in that strategy. Good at utilitarian approaches. Involved in self monitoring. It is inhibitory. Activity decreases here when jazz musicians improvise. It maintains an attentional set determines relevance. Dorsolateral Prefrontal Cortex Important for working memory lasting a few seconds to remember a phone number that was just given to you. Problems may lead to environmental dependency syndrome. Damage is localized to problems with executive decision making, not abnormal personality, social function, or aggression. Dorsolateral Prefrontal Cortex Information overload causes this area to shut down. This may explain why people who get too much information make worse and worse decisions (vacation spot, jeans, stocks...). Will power and making decisions (active control) are energies that can be depleted in an individual. Endurance can grow with practice. Our brains are not naturally equipped to integrate extremely large or disparate types of information. They evolved primarily to negotiate social situations and survive natural threats. 14

15 Temporal Lobe The temporal lobe is involved in auditory perception. It is important in understanding the meaning of words and visual symbols. It contains the hippocampus which plays a key role in long term memory. The left temporal lobe contains Wernicke s area which works in tandem with Broca s area making human language possible. The underside (ventral) part of the temporal lobe contains the fusiform gyrus, where recognition of faces takes place. Concept Cells So called concept cells have been located in the medial temporal lobe. These cells encode a single concept, like your favorite shirt, your laptop, or Jennifer Aniston. Parietal Lobe The parietal lobe has important functions regarding the integration of sensory information from various parts of the body, knowledge of numbers, and manipulation of objects. 15

16 Right Tempero Parietal Junction The temporoparietal junction (TPJ) is an area of the brain where the temporal and parietal lobes meet. This area is known to play a crucial role in self other distinction (our body in space) and theory of mind. Damage to this area has been implicated in producing out of the body experiences. It is also the spatial location of auditory hallucinations in schizophrenia. Electromagnetic disruption here has been shown to impair individual s abilities to make moral decisions. Empathy Empathy connects the neurocircuitry for social behavior, physical pain, and the ability to represent the self and others. This neural system responds to social separation and stress, borrowing physical pain circuitry to signal social pain. It promotes social affiliation and behaviors that seek to reduce the display of distress in other people. Empathy Can Be Manipulated Witnessing repeated violence can numb human s empathic response. Empathy can also be manipulated by propaganda that persuades us that a group of people are subhuman more like inanimate objects or animals than other human beings. 16

17 Criminal Responsibility? Legal perspective: The law is only concerned with behavior. Brains do not commit crimes, people commit crimes. Morse (2006) Biological perspective: All behavior is determined by the brain. Abnormal brains produce abnormal behavior, including criminal behavior. Nature or Nurture? Did you choose your genetics or your environment? Have you made any decisions that are independent of your history?. There is no meaningful distinction between a person s biology and his decision making. They are inseparable. The Forensic Bottom Line Current imaging techniques are very sensitive for finding abnormalities, but we cannot predict behavior, or any mental health diagnosis for that matter, based on brain scans. Specifically, there is no study that shows brain scan findings can predict violent crime or image intent. 17

18 The Connectome The connectome refers to a wiring diagram of the brain a mapping of all the neural connections. The idea is that the crucial functions of the brain are the result of neuronal networks. The Human Connectome Project is a 5 year NIH project, spread among two consortiums of research institutions. (Google the Human Connectome Project for more information.) 18