Cortical functions, memory, language and sleep

The central sulcus runs from the top of the hemisphere down its side, with the frontal lobe in front and the parietal lobe behind. The lateral sulcus lies above the temporal lobe.

• The lateral sulcus:
• Correct: The central sulcus:
• The parieto-occipital sulcus:

The hippocampus, part of the limbic system in the temporal lobe, is needed to form new memories of facts and events. The cerebellum coordinates movement; the amygdala judges emotional importance.

• Correct: The hippocampus:
• The cerebellum:
• The amygdala:

Neurotransmitter released from the presynaptic terminal binds to receptor proteins on the postsynaptic membrane. Opening channels that let positive ions in depolarizes the cell a little: an EPSP.

• Correct: Neurotransmitter binds to receptor proteins that let positive ions into the postsynaptic cell:
• The action potential jumps directly across the gap:
• The postsynaptic cell releases neurotransmitter back to the presynaptic cell:

Slow, effortful speech with good understanding is expressive (Broca's) aphasia, from damage to Broca's area in the lower left frontal lobe. Broca's area lies next to the motor cortex, so right-sided weakness often comes with it.

• Correct: Left lower frontal lobe: Correct. Broca's area is in the lower left frontal lobe.
• Left upper temporal lobe: Damage to Wernicke's area in the upper left temporal lobe causes fluent speech with poor understanding, the opposite pattern.
• Right parietal lobe: Right parietal damage typically causes neglect of the left side of space, not loss of speech.
• Left occipital lobe: Left occipital damage causes loss of vision in the right half of the scene, not trouble speaking.

Each primary area has one job for one side of the body. Destroying the hand area of the left precentral gyrus weakens only the right hand; sensation, the other hand and language, handled by other areas, are unchanged.

• Strength of the right hand: down. The left primary motor cortex sends commands to the muscles of the right side, and its hand area drives the right hand, so the right hand weakens.
• Strength of the left hand: no change. The left hand is controlled by the right hemisphere's motor cortex, which is undamaged.
• Ability to feel touch on the right hand: no change. Touch reaches the primary somatosensory cortex in the postcentral gyrus, behind the central sulcus, which was not damaged.
• Understanding of spoken words: no change. Understanding depends on Wernicke's area in the temporal lobe, far from the hand area of the motor strip.

The cortex given to a body part depends on how densely it is supplied with sensory receptors, not on its size. The lips have many more per square centimeter than the back, and every incoming signal needs cortical neurons to receive it, so the lips get a large area.

• The lips are closer to the brain, so their signals arrive stronger: Distance from the brain does not change signal strength; action potentials arrive at full size.
• Correct: The lips have far more sensory receptors per square centimeter than the back: Correct. Sensory receptor density sets how much cortex a body part gets.
• The back sends most of its touch signals to the cerebellum instead of to the cerebral cortex: Touch from the back reaches the somatosensory cortex too; it simply needs less cortex because it has fewer sensory receptors.
• The lips are used for speech, so they are mapped in Broca's area as well: The map in the somatosensory cortex is about sensation, and Broca's area does not receive touch signals.

The hippocampi are needed to form new declarative memories, so he has anterograde amnesia for facts and events. Procedural memory for skills uses the basal nuclei and cerebellum, so he can still improve at a practiced skill, as Henry Molaison did at mirror drawing.

• Remembering what he ate this morning: This morning's meal is a new memory of an event, which needs the hippocampi to form.
• Learning the names of new staff: New names are new facts, which need the hippocampi to form.
• Correct: Getting better at a new motor skill with daily practice: Correct. Procedural learning does not depend on the hippocampus.
• Recalling a conversation from an hour ago: A conversation an hour ago is a new memory of an event, which needs the hippocampi.

In REM sleep the EEG looks awake, the eyes dart, dreams are vivid, and brainstem neurons block the motor neurons to almost all skeletal muscles except the eye muscles and diaphragm. REM periods lengthen toward morning.

• Correct: The EEG shows fast, small waves like the awake brain: Yes. The REM EEG is fast and small, like being awake.
• Correct: Most skeletal muscles are paralyzed, but the diaphragm keeps working: Yes. The body is limp except the eye muscles and the diaphragm, so breathing continues.
• Slow, large delta waves dominate the EEG: No. Slow, large delta waves are the sign of N3, deep non-REM sleep.
• Correct: Most vivid, story-like dreams happen: Yes. Most vivid, story-like dreams happen in REM sleep.
• REM periods are longest in the first cycle of the night: No. REM periods are shortest early in the night and grow longer toward morning.

The line reaches N3 for long stretches in the first two cycles (about 0.6 to 1.2 and 2 to 2.6 hours), briefly around 4 hours, and not at all after that. Deep sleep is concentrated early in the night.

• Evenly across the night: The graph shows N3 early and absent late, not evenly spread.
• Correct: In the first three hours: Correct. Nearly all N3 falls in the first three hours.
• In the last three hours: The last three hours contain REM and N2 but no N3.
• Only during brief awakenings: Awakenings are at the top of the graph, the opposite of N3.

Touch from the left hand reaches the right hemisphere. With the corpus callosum cut, it cannot be passed to the left hemisphere, which produces speech in most people. So she cannot say "key," but the right hemisphere knows the object and guides the left hand to choose it.

• She names it at once and picks it out with either hand: Touch from one hand reaches mainly the opposite hemisphere, and without the corpus callosum it cannot be shared.
• Correct: She cannot name it, but her left hand can pick it out: Correct. The right hemisphere knows the key but cannot speak it.
• She can neither name it nor pick it out with her left hand: Sensation in the left hand is normal; it reaches the right hemisphere, which can guide the hand.
• She names it but cannot pick it out with her left hand: Naming needs the left hemisphere, which produces speech in most people, and the touch cannot reach it; the right hemisphere can still guide the left hand.

Strong, repeated activity lets calcium into the postsynaptic cell, which triggers the insertion of more glutamate receptor proteins. The same glutamate now opens more channels, giving a larger EPSP.

• Its resting membrane potential has become more negative: A more negative resting potential would move the cell further from threshold. That is not what long-term potentiation changes; the EPSP grows because more glutamate receptor proteins open.
• Its axon has been freshly myelinated: Myelin speeds conduction along an axon; it does not change the size of an EPSP at a synapse on the dendrites.
• It has stopped making receptor proteins for glutamate: Fewer receptor proteins would shrink the EPSP.
• Correct: It has more glutamate receptor proteins in its membrane: Correct. More receptor proteins mean a bigger response to the same transmitter.