Can tickling help us understand some symptoms of schizophren...
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Can tickling help us understand some symptoms of schizophren...
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[post_date] => 2024-12-28 11:50:01
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[post_content] => Practice Passage (Question 1-5)
*This passage is the property of Khan Academy and has been reformatted into an AAMC-style interface in their entirety by MedLife Mastery. MedLife Mastery does not endorse and is not an affiliate of Khan Academy.
Schizophrenia is a severe psychiatric disorder that has a variety of symptoms. One of the most commonly occurring symptoms are auditory hallucinations. Scientist believe that impaired self-recognition is a major contributing factor to the experience of auditory hallucinations. Impaired self-recognition is not only a necessary factor for auditory hallucinations to occur; the origin of these events must also be misattributed to something outside of the individual.
Normally, one cannot tickle oneself. A forward model describes why one is able to predict the consequences of one’s own actions. In a forward model, sensory inputs from the somatosensory cortex are compared to the predicted sensory feedback. When the delay between the signals is small enough, this prediction is utilized to attenuate the self-produced sensory signal. Through studies using fMRI, it is believed that this process of comparison takes place in the cerebellum. Other systems that may utilize this same type of model are: attenuations in muscle movements caused by electric shock when the muscle is voluntarily flexed or during head movement when the actual location of an object is identified by comparing the actual image on the retina with a previous instance of the image.
A group of cognitive neuroscientists were interested in whether or not this forward model could explain why patients with schizophrenia experience auditory hallucinations and created an experiment to test this model. A group of 35 patients, each with a clinical diagnosis of schizophrenia, was assigned to different groups based on whether or not the patient was currently experiencing auditory hallucinations (n=20), or had not experienced auditory hallucinations in more than two weeks (n=15). A third group of healthy age-matched subjects were also tested as a control group. Stimulation was applied to each subject’s left palm by either the researcher or the subject. The subject was then asked to rate the type of tactile stimulation perceived. The results are shown in Figure 1.
Figure 1: The mean difference in rating between stimulation produced by the experimenter or the patient. No significant difference in response was given by the patients experiencing auditory hallucinations between the self-produced and externally produced stimulation, thus its difference is near zero.
[post_title] => Can tickling help us understand some symptoms of schizophrenia?
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[question] => Which of these does NOT describe a sensation being attenuated in a forward model?
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[answer] => 3
[description] => Reason for the Correct Answer:
A forward model is likely the reason why one cannot tickle oneself.
A forward model is likely important in the determination of object location when the eyes move.
A forward model is likely attenuating some of the signal from the muscles when electric shocks stimulate the muscles externally.
Passivity experienced when a patient internally generates speech and interprets it as externally caused.
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[each_answer] => A. One cannot tickle oneself; the predicted sensation and actual sensory feedback cancel each other.
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[each_answer] => B. Voluntary arm movements can lower detection thresholds for arm muscle movements caused by electric shocks.
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[each_answer] => C. Passivity experienced when a patient internally generates speech and interprets it as externally caused.
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[each_answer] => D. When one moves one’s eyes, a copy is used to predict object location and is compared to the object’s location on the retina to determine the true location.
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[quiz_unique_key] => 3873426850
[question] => What effect did the presence of symptoms have on the subject group?
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[answer] => 2
[description] => Reason for the Correct Answer:
Only the control group did not have schizophrenia.
There were no significant differences between the group without symptoms and the control.
The group with symptoms present had the least difference between self-produced and externally produced stimulation.
The forward model predicts the consequences of an action and then attenuates the sensory effects of the action.
The group with symptoms present did not experience attenuation from a forward model when the stimulation was self-produced.
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[each_answer] => A. The effects of tactile stimulation on the group with schizophrenia was similar to the control group, when the stimulation was self-produced.
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[each_answer] => B. The group with symptoms present did not experience attenuation from a forward model when the stimulation was self-produced.
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[each_answer] => C. The group without symptoms present experienced a much larger difference than the control group, when the stimulation was self-produced.
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[each_answer] => D. The group with symptoms present described the tactile stimulation as much less tickly, compared to the control group, when the stimulation was self-produced.
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[quiz_unique_key] => 83407773
[question] => What area of the brain does the author suggest as a possible site for a forward model for the regulation of self-produced sensation?
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[answer] => 2
[description] => Reason for the Correct Answer:
The corpus callosum transfers information between the two hemispheres of the brain.
The motor cortex is responsible for the production of the tactile stimulation, but does not integrate the prediction of sensory consequences with the motor command.
The somatosensory cortex receives and interprets the sensory information from the tactile stimulation, but does not compare the predicted sensory consequences with the actual sensory stimulation.
The cerebellum most likely predicts the sensory consequences of an action in response to self-produced stimulation; subsequently, the response from the somatosensory cortex is attenuated.
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[each_answer] => A. Motor cortex
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[each_answer] => B. Cerebellum
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[each_answer] => C. Corpus callosum
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[each_answer] => D. Somatosensory cortex
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[quiz_unique_key] => 2261298308
[question] => Which type of receptor was stimulated during the experiment?
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[description] => Reason for the Correct Answer:
A baroreceptor is a type of mechanoreceptor that is located in blood vessels, which detects changes in pressure by measuring blood vessel stretch.
A proprioceptor responds to the relative position of the body in space.
A nociceptor detects stimuli that could be potentially damaging to the tissue and is often associated with pain.
A mechanoreceptor would respond to tactile stimulus such as tickling.
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[each_answer] => A. Proprioceptor
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[each_answer] => B. Mechanoreceptor
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[each_answer] => C. Nociceptor
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[each_answer] => D. Baroreceptor
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[quiz_unique_key] => 574431310
[question] => How could the researchers change this experiment to control for subjects with different levels of tactile sensation?
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[answer] => 1
[description] => Reason for the Correct Answer:
Decreasing or increasing the amount of tactile stimulation of all subjects will not help to control for subjects with different levels of sensation.
Changing the location of the stimulation may have an effect if the subject does not have sensation in a certain part of the foot; however, this will not help to control for different levels of sensation.
Measuring the two-point threshold to determine each subject’s tactile acuity would be the best way to control for subjects with different levels of tactile sensation.
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[each_answer] => A. Measure the two-point threshold to determine each subject’s tactile acuity.
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[each_answer] => B. Decrease the tactile stimulation to the just noticeable difference.
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[each_answer] => C. Test the level of tactile stimulation on different places on the foot.
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[each_answer] => D. Increase the pressure applied to all of the subjects.
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