Recent studies in sleep neuroscience have revealed the importance of REM cycles for memory formation. During these cycles, the brain...

Let's begin by understanding the meaning of this sentence. We'll use our understanding of pause points and segment the sentence as shown - understanding and assimilating the meaning of each segment bit by bit!

Sentence Structure

• Recent studies in sleep neuroscience
  • have revealed the importance of REM cycles for memory formation.

• During these cycles,
  • the brain
    • processes experiences from the day;
  • reviewing the details of multiple events
    • [?] the mind to consolidate important information into long-term memory.

Understanding the Meaning

Let's start from the beginning:

'Recent studies in sleep neuroscience have revealed the importance of REM cycles for memory formation.'

• This tells us that scientific research has shown that REM cycles (a stage of sleep) are important for how we form memories.

Now the next sentence:

'During these cycles, the brain processes experiences from the day;'

• During REM sleep, our brain is actively working through what happened during the day.
• The semicolon connects this to the next part, showing a closely related idea.

Now here's where we need to fill in the blank:

'reviewing the details of multiple events _____ the mind to consolidate important information into long-term memory.'

Let's look at our choices:

• A. allow (plural)
• B. allows (singular)
• C. are allowing (plural, progressive)
• D. have allowed (plural, present perfect)

To figure out what we need, let me identify what the subject is here:

• 'Reviewing the details of multiple events' is the subject
• This is an -ing form (reviewing) acting as a noun - it's the THING that does the allowing
• Even though 'events' is plural, the subject is really 'reviewing' - the act of reviewing
• An -ing form used as a subject is always treated as singular

What do we notice?

• The subject 'reviewing the details of multiple events' is grammatically singular
• We need a singular verb to match it
• The context is describing what generally happens during REM cycles, so we need present tense to match 'processes'

So we need B. allows - the singular present tense verb that matches our singular subject.

The complete meaning is:

• The brain processes experiences during REM sleep
• This process of reviewing multiple events allows the mind to move important information into long-term memory

GRAMMAR CONCEPT APPLIED

Subject-Verb Agreement with -ing Forms as Subjects

When an -ing form (called a gerund in grammar terms) acts as the subject of a sentence, it's always treated as singular, even if it contains plural words within the phrase:

Pattern:

• -ing form subject (singular) + singular verb

Examples:

1. "Swimming laps builds endurance."
   • Subject: "Swimming laps" (singular, even though "laps" is plural)
   • Verb: "builds" (singular)
   • Not "build" (plural)
2. "Reading many books improves vocabulary."
   • Subject: "Reading many books" (singular, even though "books" is plural)
   • Verb: "improves" (singular)
   • Not "improve" (plural)
3. In our question: "Reviewing the details of multiple events allows the mind..."
   • Subject: "Reviewing the details of multiple events" (singular, even though "events" is plural)
   • Verb: "allows" (singular)
   • Not "allow" (plural)

The key insight: The subject is the ACT of reviewing (singular), not the events themselves (plural). The -ing form is what's doing the action of allowing, so the verb must match that singular subject.