Question 1

A monkey with one deafferented limb:

Accepted Answer

A monkey with a deafferented limb does not use it because it lacks sensory feedback, even though it can still control the muscles.

Question 2

If a person suffered injury to the right motor cortex that resulted in paralysis of the left arm and later showed some evidence of recovery of function, which of the following would be a likely explanation?

Accepted Answer

Recovery of function after injury to the motor cortex is often due to the adjacent areas of the cortex taking over the damaged area's function. In this case, it is likely that the left motor cortex strengthened its control over the left arm, resulting in some recovery of function. The other options are less likely explanations. Using the right arm more would not necessarily strengthen the left arm, as the motor pathway for the left arm would still be damaged. New neurons growing in place of the damaged ones is also unlikely, as the adult brain has limited capacity for neurogenesis. Lastly, deafferentation refers to the loss of sensory input to a limb, and would not lead to recovery of motor function.

Question 3

After damage to the visual cortex, a rat no longer approaches the white card it has been trained to approach. What is the evidence that the rat has not completely forgotten the task?

Accepted Answer

The fact that the rat can relearn the task faster than it can learn to approach a black card suggests that it has retained some memory of the original task. This indicates that the rat has not completely forgotten the task, but rather has difficulty accessing or using the memory due to the damage to the visual cortex.

Question 4

A deafferented limb:

Accepted Answer

A deafferented limb is one that has lost its sensory input, meaning that it no longer receives information from the nerves that would normally provide touch, pain, pressure, temperature, and other sensations. This can occur as the result of nerve damage or injury to the spinal cord, and can result in a range of symptoms including numbness, tingling, loss of coordination, and difficulty with daily activities. It does not necessarily mean that the limb has lost its motor control, and may not be an amputated limb. Additionally, it is not related to whether an organism uses the limb spontaneously or not.

Question 5

A continuing sensation of an amputated body part is called:

Accepted Answer

The term "phantom limb" refers to the continuing sensation that an amputated body part is still attached and functioning. This sensation can include feelings of pain, itching, or movement in the missing limb.

Question 6

Because spinal injury damages many axons, ____ develop increased sensitivity to the remaining ones.

Accepted Answer

Postsynaptic neurons develop increased sensitivity to the remaining axons after spinal injury, a process known as denervation supersensitivity.

Question 7

The area of the cortex that receives input from the face is adjacent to the area of the cortex that receives input from the foot. After amputation of the foot, it is possible that a phantom limb sensation will be felt whenever the:

Accepted Answer

The fact that the area of the cortex that receives input from the face is adjacent to the area of the cortex that receives input from the foot suggests that there may be cross-talk between these adjacent areas. This means that after amputation of the foot, the brain may still be receiving signals from the face area, which could potentially result in phantom limb sensations whenever the face is touched. Therefore, choice B is the best answer. Choice A, other foot is touched, is less likely because the areas of the cortex that receive input from each foot are likely to be distinct, rather than adjacent. Choice C, face is anesthetized, would likely prevent any sensation from being felt in the face area, and thus would not trigger a phantom limb sensation. Choice D, axons from the foot regrow, is also unlikely to result in phantom limb sensations, as the foot itself is not present to receive signals from the regenerating axons.

Question 8

A cortical cell originally responded to stimulation of the middle finger. After amputation of that finger it begins responding to the second and fourth fingers. What most likely accounts for this?

Accepted Answer

This phenomenon is known as cortical reorganization and is believed to occur due to synaptic reorganization, where the neurons that previously responded to the stimulation of the middle finger start responding to the stimulation of adjacent fingers (in this case, the second and fourth fingers). This is thought to be a result of the brain adapting to changes in sensory input.

Question 9

If supersensitivity takes place, what can one expect to find regarding the number of receptors?

Accepted Answer

Supersensitivity refers to an increase in the response of a receptor to its neurotransmitter. This occurs when there's a decrease in the number or activity of a neurotransmitter. Thus, one can expect an increase in the number of receptors in the postsynaptic cell, which will result in an increased response to the neurotransmitter. Therefore, the correct answer is C - An increased number in the postsynaptic cell.

Question 10

A section of the somatosensory cortex ordinarily responds to the third finger of the left hand. If that finger is amputated, to what will the cells in this part of the cortex respond?

Accepted Answer

The cells in this part of the cortex will respond to the adjacent fingers and part of the palm that are still intact, which in this case is the second and fourth fingers and part of the palm. This is known as cortical reorganization or plasticity, where neighboring brain areas take over the functions of the amputated body part. The cells will not respond to the third finger of the right hand, and certainly not to the entire left and right hands.

Question 11

Investigators recorded activity from the cerebral cortex of monkeys that had an entire limb deafferented twelve years earlier. Much to their surprise, what did they find?

Accepted Answer

The cortical area that previously responded to the deafferented limb had reorganized to become responsive to the face, demonstrating cortical plasticity.

Question 12

Sensations from phantom limbs:

Accepted Answer

Sensations from phantom limbs are believed to be a result of brain reorganization, as the areas of the brain that previously received input from the amputated limb may now receive input from nearby areas. This results in the brain interpreting that input as coming from the missing limb, leading to sensations such as pain, tingling, or warmth. Removing more of the limb surgically is unlikely to diminish phantom limb sensations, as they are not caused by actual input from the amputated limb stump.

Question 13

After loss of sensory input from a limb, the axons representing that limb degenerate and:

Accepted Answer

When there is a loss of sensory input from a limb, the axons representing that limb degenerate and leave vacant synaptic sites at several levels of the CNS. This is known as synaptic stripping and can result in a reorganization of neural circuits.

Question 14

Denervation supersensitivity refers to an increase in:

Accepted Answer

Denervation supersensitivity occurs when a nerve loses its connections with the target organ, leading to an upregulation of receptors on the postsynaptic membrane, resulting in an increased response to the released neurotransmitter. This phenomenon is due to an increased sensitivity of the receptors and not due to an increase in production or release of neurotransmitters or growth of axon branches. Polarization of the membrane at rest is a normal physiological process and not directly related to denervation supersensitivity.

Question 15

One way to relieve the pain associated with a phantom limb is to:

Accepted Answer

The answer of One way to relieve the pain associated...

Question 16

Even _____ input produces enhanced responses.

Accepted Answer

Even mild input can produce enhanced responses, indicating that even a small or gentle stimulus can lead to a significant reaction.

Question 17

Modern methods have demonstrated that phantom limbs develop only if the relevant portion of the ____ reorganizes and becomes responsive to alternative inputs.

Accepted Answer

Phantom limbs are a phenomenon in which individuals perceive sensation or movement in a limb that has been amputated. Modern methods have shown that this occurs because the somatosensory cortex, the area of the brain responsible for processing sensory information from the body, reorganizes and becomes responsive to alternative inputs after the amputation. This leads to the sensation of a phantom limb, as the brain continues to receive signals from the area that used to correspond to the limb even though it is no longer there. Therefore, option A is the best choice. The other options are not directly involved in the development of phantom limbs.

Question 18

Suppose a finger is amputated. The part of the cerebral cortex that used to respond to that finger will:

Accepted Answer

The part of the cerebral cortex that used to respond to the amputated finger will become responsive to other fingers or part of the palm. This is known as cortical reorganization, where nearby areas in the brain take over the functions of the missing finger. Studies have shown that over time, the brain can rewire itself to adapt to the loss of a limb.

Question 19

After deafferenting a monkey's forelimb, it generally fails to use it because:

Accepted Answer

The answer of After deafferenting a monkey's forelimb, it generally...

Question 20

What is one reason for gradual behavioral recovery from brain damage?

Accepted Answer

The answer of What is one reason for gradual behavioral...

Quiz 5: Development and Plasticity of the Brain