Chapter 7: The Control of Action

Movement


An effector is a part of the body that can be moved. An alpha motor neuron takes place between the muscles and the nervous system, which is the primary interaction between the two. It start at the spinal cord and exits through the ventral root and finally ends in the muscle fibers. In order for a muscle to move and excitatory signal is activated and the other is accompanied by inhibitory signals.


Sherrington


He damaged the spinal cords in cats and dogs, which disconnected the peripheral motor structures. He wanted to see if the animals were able to move without the higher level commands. The stretch reflexes remained intact. He saw that they could alternate the movements of their hind limbs. For example: one leg flexed and the other was extended, then the first leg extended while the other flexed.


Thomas Brown


He found that movements did not require sensory signals. He sectioned spinal cords and the dorsal root and animals could still make walking movements. He called these the central pattern generators. These are neurons in the spinal cord that can carry out a sequence of actions with no external feedback signals.


Emilio Bizzi


He experimented with deafferented monkeys. They were trained in a pointing experiment, but a torque motor counteracted their movements, but the monkeys were unaware this. When the torque motor was on the limb stayed in the same place and could not move. However, if it was off the limb would quickly move to the correct location.


Apostolos Georgopoulos


He tested monkeys on the center-out task. First, the monkey had to love the lever to the center. Then a light illuminated one of the eight target positions. Then the monkey had to move the lever to the illuminated position in order to get the reward. While the monkeys were carrying out this task Georgopoulos was recording cell activity. He found that activity in the cell in the motor cortex is strongly correlated to movement rather than location and it was even the activity was even stronger when the animal moved the lever towards itself. 


Brain Machine Interface (BMI)


Monkeys have learned to move computer cursors and even prosthetic limbs just by thinking. This revolutionary idea can be a great help to those with amputated limbs. However, it is hard to move from animals to humans. 


Rizzolatti


He studied monkeys and studied whether or not neurons activated while observing someone carry out an action. The neurons in monkeys responded similarly when the monkey cracked the peanut itself,  watched someone crack it, watch someone crack it but could not hear it and could hear the peanut being cracked but could not see it. He called these mirror neurons.


Planning and Execution of Movement


Individuals were taught a complex sequence of finger movements. When TMS is used to disrupt the motor cortex the individual knew what to do but something stopped them. When the supplementary motor area was disrupted they lost track and could not remember the goal. However, activation depends on how much it is based on memory. How well you know a certain action changes in the brain. A novel action start in the PMC but when you start to know something better it moves to the SMA.


Apraxia


Apraxia is a loss of motor skills. These individuals are not able to turn their thoughts into actions. One example is of a patient with bilateral lesions of the parietal lobes. She was a fish filleter and one days she started to cut the fish when she all of a sudden stopped. She remembered how she needed to finish the task but she just could not execute it. 
Ideomotor apraxia is when the individual has an idea of the action but they cannot execute it properly. Ideation apraxia is more severe. It is when the patient's knowledge of an action is disrupted.


Basal Ganglia


The basal ganglia consists of five nuclei: caudate nucleus, putamen, globus pallidus, subthalamic nucleus and the substantia nigra. In Parkinson's disease the pathway from the substantia nigra to the striatum is destroyed. The substantia nigra produces most of the body's dopamine. This produces more excitation from the thalamus to the cortex, when then causes uncontrollable movements. There are two kinds of dopamine receptors, when one has Parkinson's the dopamine cannot cross the blood brain barrier. The medication one can take is called L-dopa. It is one step back from dopamine so it is able to cross the blood brain barrier. 


Those with Parkinson's have a motor impairment as well as a cognitive impairment.  Steven Keele tested patients in a shifting test. They had to learn two 3 movement sequence. Then they were asked to produce a six element sequence from the two movement sequences that they learned initially. Parkinson's patients had a hard time when they had to transition between sequences. This shows that they have a motor control impairment. Then they were tested on their cognition. They had to discriminate between either shapes or colors and they reaction time was recorded. Again, they were slow when they had to shift.

Chapter 6: Object Recognition

Agnosia: is a failure of perception, or “to experience a failure of knowledge”. For some, they are not able to develop a rational percept; others are not able to access the knowledge to identify an object.

Cortical Pathways

 The occipitotemporal pathway is for object perception and recognition. The occipitoparietal pathway is for spatial perception or determining where an object is. Typically, the parietal and periphery determine “where” and the temporal and fovea help to determine “what”.

Object Recognition

Apperceptive Agnosia: failure to recognize an object. One study tested people with apperceptive agonsia to see how well they are able to recognize an incomplete picture. Typically, they are not able to tell what they picture is until it is complete. Reseachers found that there is more of a deficit when the right hemisphere is damaged than the left hemisphere. Warrington also gave the Unusual Views Object Test to those with apperceptive agnosia and found that they are not able to recognize and object that is shown to them in an unusual view.

Associative Agnosia: have the correct information but are not able to access it. One study found that those with associative agnosia could point out an object when they were named but could not point out the object when asked if they were different.

Prosopagnosia: the inability to recognize faces. Not only can a damaged brain cause prosopagnosia, but genes also play a role in this.  Two regions of the temporal lobe a activiated while looking at faces: the superior temporal sulcus and the inferotemporal gyrus.

Chapter 5: Sensation and Perception

Olfactory Perception

The sense of smell is more primitive than any other senses we have. First, the odor molecules enter the nasal cavity. The odorants attach to the olfactory epithelium, which are odor receptors. There are thousands of odor receptors; each respond to certain number of odorants. When an odorant binds to a bipolar neuron, also known as an olfactory receptor, a signal is sent to the neurons in the olfactory bulb, which are called glomeruli. They then leave the olfactory bulb and go to the primary olfactory cortex. The primary olfactory cortex is located at the intersection of the frontal and temporal cortices. Then the neurons in this area connect to the orbitofrontal cortex, which is considered the secondary olfactory processing center.

There are a few reasons why olfactory perception has not been studied as much as the other senses. It is hard to control how much of an odor you are giving to a participant. It is also hard to know when an odor is no longer present. Most odors are quite subtle and take investigating to identify and detect the smell.

Vision

Vision is the most studied out of all the senses. Visual information is in the light reflected from objects. As light passes through the eye, the image in inverted and projects on the retina. Photoreceptors can be found in the deepest layer of the retina. There are two types of photoreceptors: rods and cones. Rods are most effective with lower levels of light; however, cones are sensitive to higher levels of light. The fovea contains many cones. The optic nerve transmits visual information to the central nervous system. Since the retina is curved the temporal half of either the left or right retina is stimulated by the opposite visual field. Each optic nerve splits into different pathways depending where they terminate in the subcortex. Most of the axons are projected from the retina to the lateral geniculate nucleus. The remaining axons stimulate other subcortical structures.  The final projection to the visual cortex is through the geniculocortical pathway and then heads to the primary visual cortex.

The area that is activated in the color foci is called area V4 and the area activated in the motion task is area V5. There is a big difference between species when it comes to the position of the color and motion areas in the brain.

Achromatopsia is a deficit in seeing color. People with achromatopsia have lesions around the V4 area. One study found that individuals are better at differing reflectance differences than they are at distinguishing hue differences. Each subject was shown three color patches. Two of them were identical and the third was different in either hue or reflectance.

Akinetopsia is a deficit in motion perception. M.P. could not see objects moving at a continual speed; instead, she saw an object in one position and then another. She was not able to determine the direction or speed of a moving object. The area in the brain that was damaged was the area around the V5.

Chapter 4: Methods of Cognitive Neuroscience

Mental Representations in the Cognitive Approach


There are two key concepts that guide the cognitive approach. The first is: how we process information depends on what we know and the second: mental representations change over time. The Posner experiment showed that we can determine many representations of a stimuli (the physical aspect of the stimulus, the stimuli's identity and finally the category that the stimulus belongs too).


Another goal of cognitive psychology is to figure out how we perform tasks. Sternberg proposed four primary mental operations:


1. Encode: identify the object
2. Compare: the object with the objects stored in memory
3. Decide: if the object matches the items in memory
4. Respond: make a decision


How efficient is our brain at retrieving information? Two ideas were proposed: (1) if this is a parallel process then the reaction time should be independent of the number of objects in your memory (2) if it is a serial or sequential process reaction time should slow down as the memory set increases. Sternberg found that reaction time increased as the memory set increased.


Computer Modeling


Computer simulations are used to mimic the cognitive processes and that support a particular behavior. In order for this to be successful the creator must be very specific about how the information is represented and changes. Computer models show that minor changes in the brain could result in big behavior changes. People are even able to damage areas in the computer model to see how that affects behavior.


Animals in Experiments


Single-cell recording was a big breakthrough for Cognitive Psychology. In order to do single-cell recording, one must stick an electrode into a single. However, it may be hard to observe behavior because this technique may kill the cell. This technique has been used to study most regions of the brain. Many studies have looked into the visual systems. All cells that are visually sensitive can only respond to a stimuli in a certain region of space; this is called the receptive field.. The receptive field for cells vary; the smallest are in the primary visual cortex and the largest are in the association visual cortex.


Genetics play a role in cognitive function. Right now, neuroscientists  are working with animals  to identify  the genetic mechanisms in both the brain structure and function. Some are performing knockout procedures. This means that certain genes are manipulated so that they are know longer able to function.


Neurology


Most neurological studies see how much damage has been done and how it was done. Then they measure electrical activity and changes in behavior. Diffusion tensor imaging is done with  an MRI scanner. It looks at how big and active pathways are.


How does cognitive psychology play into neurology? If a patient has damage cognitive psychology can define the nature of the impairment. Obviously, if damage is done in a certain brain area and a behavior depends on that area the damage should disrupt the behavior. Single a double dissociations are helpful in studying damaged brain areas and cognitive tasks. In a single dissociation, two groups are tested on two tasks and there should be a difference between the groups. In a double dissociation, three groups are compared. One is a control group, group one is impaired at task A and group two is impaired at task B.


Localizing a certain area for a specific deficit is harder to do in groups. This is because no one has damage in the exact same area, psychologists have to isolate the a common area in order to pinpoint a certain damaged area for a certain deficit. However, with individuals you are able to focus on the one brain area that is damaged and understand that specific damaged area. Many wonder if the damage is specific to the individual or are you able to generalize it across people.