Neuroanatomy. Cerebral Cortex: Movement and Speech

Size: px

Start display at page:

Download "Neuroanatomy. Cerebral Cortex: Movement and Speech"

Jacob Singleton
5 years ago
Views:

1 Neuroanatomy Cerebral Cortex: Movement and Speech

Functional Neuroanatomy Phrenology: Pseudoscience Functional neuroanatomy is the study of how different parts of the brain control different aspects of behavior.

One of the earliest ways of studying brain function was quackery called phrenology.

2 Functional Neuroanatomy Phrenology: Pseudoscience Functional neuroanatomy is the study of how different parts of the brain control different aspects of behavior. It s only in the last couple hundred years that people have really begun to appreciate that behaviors are localized to different parts of the brain. One of the earliest ways of studying brain function was quackery called phrenology. According to phrenology, different parts of the brain controlled different aspects of behavior and personality (this part is true) and our abilities and behaviors are determined by how developed those areas are. Phrenologists would feel the heads of patients in order to see what brain areas were most developed, figuring that well-developed brain areas would be associated with bumps on the head and underdeveloped areas would be associated with dents. While phrenology is baloney, it was important because it got science thinking about the idea of localizing functions in the brain.

This involved drilling a hole, pouring in blasting powder, covering the powder with sand or other wadding, then firmly tamping the explosives with a long steel rod before igniting the mixture.

3 Functional Neuroanatomy Another historically important event for functional neuroanatomy is the story of Phineas Gage. Phineas Gage was a foreman on a railroad construction crew in the mid-19 th century. As part of their duties, the crew had to clear the way for the railroad with explosives. This involved drilling a hole, pouring in blasting powder, covering the powder with sand or other wadding, then firmly tamping the explosives with a long steel rod before igniting the mixture. Obviously a hazardous job! Unfortunately, Gage somehow forgot to put the sand in on one fateful day. When he went to tamp the explosives, they ignited, turning his tamping rod into a projectile. It went right through his head, entering just under his left eye and coming out the top of his head. He went into convulsions but somehow survived the accident. He was able to walk and talk normally shortly after the accident. Despite severe brain damage, he seemed behaviorally normal at first (except, of course, for the physical damage to his head and face he was blinded in the left eye, for example). As the story goes, though, Gage s personality was dramatically changed by the accident. While he was previously a respectable, well-liked, hard-working man, afterwards he was said to be rude, violent, and unemployable. Clearly, the damage to his brain had altered his very personality! It turns out that while his personality probably was changed for a little while, he probably recovered his social abilities and became more-or-less normal. Despite being more of a fairy tale than a true story, the story of Phineas Gage is still very important in the history of neurology because it launched a lot of interest in localizing brain function.

Functional Neuroanatomy The Brain Brainstem Diencephalon Cerebral cortex Cerebellum Very generally speaking, we can divide the brain into four general parts : The brainstem: This is the stalk that

4 Functional Neuroanatomy The Brain Brainstem Diencephalon Cerebral cortex Cerebellum Very generally speaking, we can divide the brain into four general parts : The brainstem: This is the stalk that the rest of the brain sits on top of. It controls our most basic vegetative life-support functions: heart rate, breathing, alertness, digestion, vomiting, etc. It also has a lot of tracts carrying impulses to and from the higher brain centers. The diencephalon: Sitting on top of the brainstem, the diencephalon is responsible for more complex life-support functions such as motivational behaviors (hunger, thirst, sex drive, etc.) and hormone control. It also routes sensory signals to the correct nuclei in the cortex. The cerebral cortex (or cerebrum): The highly-folded part of the brain that wraps around the diencephalon and brainstem ( cortex means covering ). This is where all of our thinking, memory, and conscious awareness, and voluntary behaviors happen. The rest of this lecture covers the cortex in more detail. The cerebellum ( little brain ): The cerebellum is a separate structure attached to the rest of the brain on the posterior-inferior side. It is involved in coordinating and controlling movements, timing of muscle voluntary movements, and well-learned motor behaviors.

Features Cerebral hemispheres Corpus callosum The word cortex means covering, an appropriate name considering the cortex covers the diencephalon and brainstem.

5 Features Cerebral hemispheres Corpus callosum The word cortex means covering, an appropriate name considering the cortex covers the diencephalon and brainstem. (That s not it s job; that s just where it s located). The cortex includes neurons that handle voluntary movement, thinking, planning, reasoning, personality, emotion, associations, and other higher-order cognitive functions. Structurally, the cortex is divided into two hemispheres: a left hemisphere and the right hemisphere. The two hemispheres are separated by a deep rift called the longitudinal fissure and communicate with one another across a huge slugshaped band of axons called the corpus callosum. 5

6 Features Gyri, sulci, & fissures Major landmarks When you look at the cortex, you ll noticed that it s not a smooth surface: it has lots of folds, hills, and wrinkles. The raised parts of the cortex (the hills) are called gyri (singular: gyrus). The folds between gyri are called sulci (singular: sulcus). A verydeep sulcus is sometimes called a fissure.every gyrus and sulcus has a name, but you re only responsible for memorizing a few. As already mentioned, the deep fissure that separates the right and left hemispheres is called the longitudinal fissure. The long sulcus that separates the frontal from the parietal lobe is the central sulcus and it is bordered by the precentral gyrus on the anterior side and the postcentral gyrus on the posterior side. The horizontal sulcus that divides the temporal lobe from the frontal and parietal lobes is the longitudinal sulcus (or longitudinal fissure). 6

7 Features Major landmarks Central Sulcus, Lateral sulcus Precentral gyrus, postcentral gyrus Longitudinal Fissure See if you can identify all of the major landmarks in these pictures. In the numbered picture, precentral gyrus is number 12, postcentral gyrus is number 13, and the central sulcus separates them. The lateral fissure is the sulcus between numbers 13 and 18. 7

8 Features Cortical Lobes (insula underneath) The major sulci of the cortex visually divide the brain into 5 different regions that we call lobes. The frontal lobe consists of all the cortex anterior to the central sulcus. It is involved in voluntary motor control, planning and learning movements, learning skills, personality, emotions, social behavior, planning, reasoning, judgement, etc. Posterior to central sulcus is parietal lobe. The parietal lobe is involved in perception of the general senses, identifying things by touch, and recognizing objects visually. Inferior to the lateral fissure is the temporal lobe, which is involved in perception of smell and hearing, understanding speech, forming new memories, and emotion. The most posterior part of the cortex is the occipital lobe, which is involved in visual perception and processing visual associations. Finally, the more-basic insula is a lobe of the brain not visible from the outside. It s involved in more basic associations, strong emotions (fear, rage, etc.), and perception of balance and taste. 8

9 Features Cortical Lobes Try to identify each lobe of the brain in this picture. 9

10 Cortical Functions To some extent, different regions of the cortex are responsible for different behavioral functions. 10

11 Cortical Functions Motor, sensory, and association areas Mostly contralateral Lateralization Generally speaking, we can categorize each functional area of the cortex as motor (plans or initiates voluntary movement), sensory (involved in perception or processing of sensory information), or association (connects sensory information to previous memories recognizing things, for example). For the most part, motor and sensory pathways show contralateral organization. This means that the skin and muscles on the left side of the body are handled by the right hemisphere of the brain and vice-versa. Olfaction is an exception to this rule. It shows ipsilateral organization. Many behavior functions show lateralization. This means that they are represented completely or mostly in just one hemisphere of the cortex. For example, speech production is lateralized in most people in the left hemisphere. The analogous region of the brain in the right hemisphere is involved in adding inflection and emotion to the voice. 11

Cortical Functions Somatic sensory area Parietal lobe/postcentral gyrus General senses Sensory homunculus Somatosensory association area Let s examine a few functional areas of the brain.

Since different regions of somatosensory cortex correspond to sensory receptors from specific parts of the body, we can make a sort of map of the body on the brain. We call this a corticotropic map.

12 Cortical Functions Somatic sensory area Parietal lobe/postcentral gyrus General senses Sensory homunculus Somatosensory association area Let s examine a few functional areas of the brain. The somatic sensory area (also called somatosensory cortex) covers the entire postcentral gyrus. It is involved in perception of the general senses (pressure, pain and temperature). Since different regions of somatosensory cortex correspond to sensory receptors from specific parts of the body, we can make a sort of map of the body on the brain. We call this a corticotropic map. However, some regions of the skin are more sensitive than other regions of the skin some regions are lots of brain dedicated to them (such as the lips and the fingers) while others have less (such as the back and the legs). A model of how much brain is dedicated to each region of the skin is called a sensory homunculus (see the next slide). Posterior to somatosensory cortex in the parietal lobe, we have the somatosensory association areas. This part of the brain is responsible for connecting our current touch sensations with our memories. It s what allows us to recognize an object based on how it feels. 12

13 Cortical Functions This is a sculpture of a sensory homunculus. Which regions have very sensitive touch? Which have less sensitive touch? 13

Cortical Functions Primary motor area Frontal lobe/ precentral gyrus Corticospinal tracts/ pyramids Motor homunculus Premotor area Just anterior to somatosensory cortex, covering the precentral gyrus

14 Cortical Functions Primary motor area Frontal lobe/ precentral gyrus Corticospinal tracts/ pyramids Motor homunculus Premotor area Just anterior to somatosensory cortex, covering the precentral gyrus in the frontal lobe, is the primary motor area. This is where all of the body s voluntary movements are initiated. Like the somatosensory cortex, primary motor cortex has different areas that control muscles from specific muscles and, like somatosensory cortex, the top of the body is represented on the inferior and lateral parts of the cortex while the lower parts of the body are represented on the superior and medial parts of the cortex. Primary motor cortex has a homunculus similar to that of somatosensory cortex: the parts of the body where we have very good dexterity (lots of neurons, each controlling very small motor units) have a lot of brain dedicated to them while parts where we have poor dexterity (few large motor units) have less brain dedicated. Anterior to primary motor cortex, we have the premotor area. This is the region of the brain that plans out movements and learns motor skills. If premotor area becomes damaged, we may lose motor skills such as typing, driving a car, etc., but the skills can be relearned. 14

15 Cortical Functions This a motor homunculus. 15

16 Cortical Functions Identify all the brain regions discussed so far. 16

Cortical Functions Language & Speech areas Broca s area (Frontal lobe) Wernicke s area (Temporal lobe) Arcuate fasciculus (Connection) Aphasias Speech and language are processed and produced in some

17 Cortical Functions Language & Speech areas Broca s area (Frontal lobe) Wernicke s area (Temporal lobe) Arcuate fasciculus (Connection) Aphasias Speech and language are processed and produced in some very specific parts of the cortex. A part of the brain called Broca s area is responsible for producing speech. It s found in the frontal lobe near the part of primary motor cortex that controls the muscles of the tongue, mouth and throat. The part of the brain responsible for speech comprehension is called Wernicke s area. It s found in the temporal lobe, very near the part of the brain that perceives sound. Wernicke s area is connected to Broca s area by a band of fibers called the arculate fasciculus. In most people, speech production and comprehension are highly lateralized. We call the hemisphere of the brain where Broca s and Wernicke s areas are found the dominant hemisphere. In most people, this is the left hemisphere. In the nondominant hemisphere, the analogs of Broca s and Wernicke s areas are involved in producing or understanding the tone of speech (inflections, sarcasm, etc.) A deficit in speech production or comprehension as a result of brain damage is called an aphasia. There are several types of aphasias, but here are the three most straightforward: Broca s aphasia: Caused by damage to Broca s area. Speech production is very difficult (non-fluent), but understanding of speech is preserved. Sometimes patients are still able to write, sometimes not. Speech is telegraphic (very short), but it does make sense. Wernicke s aphasia: Caused by damage to Wernicke s area. Characterized by an inability to understand language or read as well as an inability to produce meaningful speech. Speech is fluent, but nonsensical. Conduction aphasia: Caused by damage to the arcuate fasciculus. Speech production and comprehension are normal, but patients are unable to repeat spoken language or read aloud. 17

18 Cortical Functions To look for aphasias and determine the extent of damage, patients are presented with pictures such as this one and asked to describe what s going on. 18

19 Broca s Aphasia Examiner: Describe this picture. Patient: kid kk can cookie caandy well I don t t know but it s s writ easy does it slam early fall men many no girl. Dishes soap water water falling pah that s s all dish that s s all. Cookies can candy cookies cookies he down That s s all. Girl slipping water water and it hurts much to do. Her clean up. Dishes up there I think that s doing it Examiner: What is she doing with the dishes? Patient: discharge no I forgot dirtying clothes [?] dish {?} water Examiner: What about it? Patient: slippery water [?] scolded slipped

20 Broca s Aphasia Examiner: Describe this picture. Patient: uh mother and dad no mother dishes uh runnin[g] ] over water and floor and they uh wipin[g] dis[h]es and uh two kids uh stool and cookie cookie jar uh cabinet and stool uh tippin[g] ] over and uh bad and somebody gonna get hurt.

21 Wernicke s Aphasia Clinician: Tell me where you live. Patient: Well, it s s a meender place and it has two two of them. For dreaming and pinding after supper. And up and down. Four of down and three of up (Brookshire 2003:155) Clinician: What s s the weather like today? Patient: Fully under the jimjam and on the altigrabber. (Brookshire 2003:155)

22 Wernicke s Aphasia Patient is asked what brought him to the hospital. Is this some of the work that we work as we did before? All right From when wine [why] I m I m here. What s s wrong with me because I was myself until the taenz took something about the time between me and my regular time in that time and they took the time in that time here and that s s when the the time took around here and saw me around in it s s started with me no time and I bekan [began] work of nothing else that s s the way the doctor find me that way (Obler & Gjerlow 1999:43)

23 Cortical Functions Identify all the major cortical areas discussed. 23

24 Cortical Functions Special Sensory Areas Visual cortex (occipital lobe) Auditory cortex (temporal lobe) Olfactory cortex (temporal lobe) Gustatory cortex (insula) Equilibrium cortex (insula) All of the special senses have cortical regions involved in perception. Visual cortex is located in the occipital lobe. Auditory (hearing) and olfactory (smelling) cortices are located in the temoporal lobe. Gustatory (taste) and equilibrium (balance) cortices are located in the insula. 24

Neocortex. Hemispheres 9/22/2010. Psychology 472 Pharmacology of Psychoactive Drugs. Structures are divided into several section or lobes.

Neocortex. Hemispheres 9/22/2010. Psychology 472 Pharmacology of Psychoactive Drugs. Structures are divided into several section or lobes. Neocortex Psychology 472 Pharmacology of Psychoactive Drugs 1 Is the most developed in Humans Has many folds and fissures The folds of tissue are called gyri or a gyrus (single) The fissures or valleys