How the Brain Studies Action
One of those methods is behavioral, in which, video and audio equipments allows one to record the position of body parts in space and time. This can be used to measure speed, accuracy, and kinematics, which include velocity and acceleration. One can systematically investigate the output of the action system with this procedure.
Many use muscle physiology to study actions as well. With this, activity of individual muscles or muscle fibers during action can be measured in various and valuable ways. According to the University of Oregon, the number of muscle fibers in the body can range from 5-10 to > 100. One major strength of this method is its ability to help us better understand how muscles work. We already know they are responsible for positioning and movement of the skeleton, however in an experimental setting, we can learn more specific concepts involved with them. However, both behavioral and muscle physiology do not tell us anything about the brain.
According to Clinical neurophysiology online, neurophysiology is the study of nervous system functions within a clinical setting. With this method, electrodes are implanted in the brain and activity of individual neurons is recorded. Electroencephalography (EEG), electromyography (EMG), somatosensory evoked potentials (SSEP), motor evoked potentials (MEP), and brain stem auditory evoked responses (BAER) are utilized for this method. Neurophysiology is fascinating because of its ability to take record of a number of neurons and measure their activity in real time and allows for spatial and temporal resolution.
Another method involves putting a subject in a brain scanner and measuring the amount of blood flow that occurs through various tasks. Neuro-imaging is a method of studying actions that allows for direct measure of activity within the brain. Brain flow is directly related to the level of activity occurring. The downfall to this method is that many of these processes take less than 2-4 seconds and this makes it difficult to measure these movements on a scanner. The weakness of both neurophysiology and neuroimaging is that both include the amount of time that actions occurs and how to measure them effectively.
By examining the consequences of brain damage in humans and animals, neuropsychology can decide whether the damage measured in one area is linked to a behavioral deficit. Then, one can assume that the damaged area is needed for that function. This allows for the examination of consequences (in humans) with naturally-occurring brain damage. The strengths involved with this method is that it shows what is most important for a particular function. However, it cannot place lesions where they are wanted and are not able to size them as well.
With Transcranial magnetic stimulation (TMS), a high-powered magnetic coil temporarily disrupts the brain’s activity in healthy humans (or animals). This procedure is more ethical then giving people brain damage. However, not all areas can be tested, only those found on the surface of the brain. One must be careful not to give the participant a seizure with this method. In a 2005 Psychiatry Clinical Neuroscience article, it was reported that TMS can be used in the treatment of depression. This was discovered through a pilot study of 23 patients meeting with the Diagnostic and Statistic Manual of Mental Disorders, in which a single-pulse TMS may show for a possible antidepressive effect. Depression symptoms were measured on a Hamilton Rating Scale for Depression. During the study, patients were given a series of 10 stimuli over the frontal area of both sides of their head (total of 20). This occurred for a series of 5 days.
In the present SPECT (single-photon emission computed tomography), six of the target patients used to study these effects shows results on their local blood flow volume. The SPECT results showed regional cerebral blood flow in the bilateral frontal region had increased in 4 out of 6 patients when compared as the experiment lasted. Conclusions were made that with this study in which the single-pulse TMS was used, this may possess a variety of antidepressive effects without creating adverse reactions to the patients. These findings could be influential in the treatment of depression in the near future.
A mathematical method with neglect is computational modeling. It is used to devise various models on how actions must be carried out by specific neurons. The positive aspect of this method is that it allows one to approach the question of brain function from a synthetic rather than an analytical perspective. However, the method is not as effective as other provided. Event-related potential record electrical activity from the scalp. This allows for good temporal resolution. However, allows for poor spatial resolution, which leaves you with the question of what you are actually recording.
While studying action within the brain, one must understand two recent theories of action – perception-action and planning-control. Perception-action, according to Milner & Goodale (1995), relies on different parts of the brains. It uses different visual
information by identifying objects on comparison of what is seen and what is actually stored in one’s memory. Action is equivalent to the moment to moment computations of a target’s relation to a body.
In The Visual Brain in Action by A. David Milner, studies involving the visual properties of neurons in the ventral and dorsal streams became a source of evidence for the Perception-Action method. These neurons are attuned to specific objective features, which shows for specificity within categories. This study also focuses on the idea that the ventral stream is especially concerning with the significance of specific object than just with moment-to-moment changes in the visual areas.
The neurons studied shows different properties than the ventral stream did. These visual properties were only discovered after specific experimental advances allowed the experimenter to record subjects performing certain visuomotor tasks. These actions were affected by visual stimuli because of various responses from the subjects. For example, some cells respond differently when stimulus are within a target’s reach; with others when it is the object of a grasp response; others when it is moving and following by a eye movement; and others when it is stationary and the object of a ocular fixation.
Also, there are many cells within the dorsal stream as well as the ventral stream, that passively are activated by visual stimuli – – certain logic however requires that these neuron receive certain visual inputs from specific cells that are not visuomotor type. One important characteristic of many PP neurons is their quick respond to visual stimulus. This procedure is known as neuronal enhancement.
Perception is affected by factors such as color and form that are coded in one’s P cells. Action is directly sensitive to both the motion and orientation that can be found in one’s M cells. The brain’s activity in one’s ventral and dorsal streams is associated with perception and action. The strengths of this method include the simplistic and straightforwardness of finding results. It also accommodates a good amount of behavioral and neurological data and allows for a variety of predicting options. However, many argue that it is often too simple and straightforward for feasible results; it also cannot explain the subtleties in the findings.
The planning vs. control method uses motor programs (a set of stored muscle commands called from memory) to plan and initiate movement. Control uses visual and proprioceptive feedback that guides the hand in flight. This method tends to be slow and involves visual information. Control is faster and relies on more simple information.
This is affected by cognitive factors such as illusions and semantics, and online control will not be. Activity is related to planning and control that follows an inferior-superior gradient in the partial lobes. Words can also be affected by these early partitions of action, but not later ones. This method allows for a better account of findings.
Various studies involving monkeys have drawn various conclusions about the parietal lobe and various actions. For example, certain functional specializations within the lobe have been discovered with hand versus eye movement or grasping versus pointing. Reaching and grasping relies on different types of information. With reaching, extrinistic object properties are important such as distance, position and velocity. While with grasping, intrinistic properties are affected such as size, shape and weight.
Reaching (arm) and grasping (hand) has very consistent results involving velocity and acceleration. After one’s hand begins to move, velocity peaks halfway between then and when the hand has reached its target. With acceleration, the amount increases greatly after the hand begins to move and then slows down considerably right before it reaches it target. The unfolding of kinematic movement varies within the characteristics of the target and the relation between the target and the hand.
In Scott Glover’s “Separate Visual Representations in the Planning and Control of Action,” he explains that the ability of our body to disregard motion of images during eye movements makes it very difficult for us to notice small displacements that occur in our visual world. In turn, this would effect more of an intrinsic effect such of that as the grasping movement which is affected by size in particular. These objects can be moved several degrees without the conscious noticing. In Table 2 of his report, he compares the visual feedback and effect on action on various movements. With no vision, the degree of perception was always a higher degree (up to 2 degrees), which draws a conclusion that one’s extrinistic values that are directly affected with the reaching aspect are better understood in the conscious state.
With various attempts at discovering the most effective way of studying this disease, scientists are given the opportunity to learn many things by working hands-on with it. With all these experiments, a positive result will occur in which patients can be assured that their disease is valid and understood on various levels.
