Chapter 46

1. 1. The conscious sensory (afferent) stimulus of seeing a venomous snake prompts voluntary commands in the CNS to the muscles in the legs (efferent output) to run from the danger.

   2. The conscious sensory stimulus of the aroma of freshly baked bread can stimulate the autonomic responses of salivation and increased stomach activity.

   3. The unconscious stimulus of a fall in blood pressure can cause an involuntary command to increase heart rate.

2. Failure of the anterior region of the neural tube to close has the greatest effect on the telencephalon and results in lack of development of the cerebrum.

3. Areas of association cortex involved in reading and language are situated between the visual area in the occipital cortex and the auditory area in the temporal cortex. Reading integrates interpretation of visual images with the auditory patterns of spoken language.

4. Areas of the body that are shown by the two-point spatial discrimination test to be highly sensitive to touch are represented by large areas of somatosensory cortex.

5. The comparison of cortical capacity of humans with that of other mammals cannot be based just on brain size, because the human cortex is highly convoluted, giving the cortex a larger area. A higher percentage of the human cortex is devoted to association functions (association cortex) that increase cortical capacity.

1. A knife wound to the left side of the neck could sever the sympathetic chain of ganglia on that side. This could break the connection between the preganglionic and postganglionic sympathetic neurons that innervate the pupil of the left eye and cause it to dilate.

2. A small spot of light on the retina can illuminate just the on-center of the receptive field of a ganglion cell and therefore activate it maximally. A larger spot of light would illuminate receptor cells around the on-center that have an inhibitory influence, and therefore decrease the activation caused by illuminating the center of that receptive field.

3. If the optic chiasm were cut right on the midline, the axons from the ganglion cells in the medial halves of the retina would not cross over to the opposite sides of the brain. As a result, the left eye would not see things in the left visual field and the right eye would not see things in the right visual field. Without input from both eyes, there would be no binocular cells and therefore no depth perception.

1. Paralysis of skeletal muscles during REM sleep prevents the possibility that an individual would act out his or her dreams while in the dreaming state.

2. A person with a severed corpus callosum would not be able to describe in words an object in his left visual field, but he could draw it or point to a similar object in a picture.

3. Since H.M. was capable of immediate memory but could not retain longer-term declarative memories, we can conclude that the hippocampus is necessary for acquiring new declarative experiences and consolidating them into long-term memory.

4. Humans, great apes, elephants, and some marine mammals have an expanded insular lobe, which is involved in integrating physiological information from throughout the body, as well as social and emotional information, and may therefore generate a sense of self-awareness.

1. The probability of this sequence out of a random firing of nine cells is first a function of the probability of that one combination from all of the combinations of cells that could constitute six elements of the nine possible. That would be 1/(9 × 8 × 7 × 6 × 5 × 4) = 1/60,480 = 1.6 × 10^–5. Then, for the sequence, what is the probability that it would be in the correct order? There is one possible correct order of those six elements in 6 × 5 × 4 × 3 × 2 × 1 possible combinations or 1 in 720, thus the probability would be 1.4 × 10^–3. So the probability of recording those specific six elements out of nine in the correct order would be 2.24 × 10^–8.

2. A-48

   The probability of recording four elements in the sequence in the proper order would be: 1/(9 × 8 × 7 × 6) = 1/4,698 = 2.1 × 10^–4, and the probability of getting those four elements in the proper order would be 1/24. Thus the probability of recording those specific four elements out of nine in the correct order would be 2.1 × 10^–4 × 0.042 = 0.88 × 10^–3.

3. Both of these recordings have a probability of < 0.01, so they would be considered significant low-probability events.

4. The time frame of the sequence recording during sleep is about five times faster than the occurrence of that sequence during wakefulness when the rat is running the maze.

1. The subjects who were well rested gave correct answers to working-memory tests at least 95 percent of the time. Sleep-deprived subjects were almost 10 percent more likely to give incorrect answers.

2. Compared with well-rested subjects, sleep-deprived subjects took approximately 50 milliseconds longer to answer the questions, which could reflect decreased alertness. The results could also be due to an effect of sleep deprivation on cognitive processing time.

3. The left side of the cerebral cortex is responsible for processing and understanding language. Since the tests involved letter recognition and sequencing, this is likely to be the area most activated by the tests.

4. Sleep deprivation caused a 20−30 percent decrease in parietal lobe activity but only a 10−15 percent decline in prefrontal lobe activity. Testing this conclusion would require a statistical evaluation of the differences between activities in the two brain areas as a function of the sleep-deprivation treatment.