From the Guidelines
Yes, rhythmic midtemporal theta activity of drowsiness can occur during stage N2 (Non-Rapid Eye Movement) sleep. This phenomenon is characterized by rhythmic 4-7 Hz theta activity that appears predominantly in the temporal regions, and is also known as psychomotor variant pattern. Although the provided evidence does not directly address the occurrence of rhythmic midtemporal theta activity during stage N2 sleep, it discusses the changes in sleep architecture following the AASM sleep scoring rules, including a mean decrease in NREM 2 sleep 1. Some key points to consider include:
- Rhythmic midtemporal theta activity is a benign normal variant that typically emerges during drowsiness and can persist into lighter stages of sleep, including N2.
- During N2 sleep, which is characterized by sleep spindles and K-complexes, rhythmic midtemporal theta activity may continue to appear intermittently 1.
- The physiological basis for this activity involves normal synchronization of neuronal networks in temporal regions during decreased alertness.
- Clinicians should recognize this pattern to avoid misinterpreting it as pathological activity, as no treatment is required for this normal electrographic phenomenon. Key aspects of N2 sleep and rhythmic midtemporal theta activity include:
- N2 sleep is characterized by specific electroencephalographic features, such as sleep spindles and K-complexes.
- Rhythmic midtemporal theta activity is distinct from these features, but can co-occur with them during N2 sleep.
- Accurate identification of this activity is essential to avoid misdiagnosis and unnecessary treatment.
From the Research
Rhythmic Midtemporal Theta Activity of Drowsiness
- Rhythmic midtemporal theta activity of drowsiness can occur during stage N2 (Non-Rapid Eye Movement) sleep, as evidenced by studies that have observed theta bursts preceding downstates in N2 sleep 2.
- The occurrence of rhythmic midtemporal theta bursts of drowsiness (RMTD) during N2 sleep has been reported, with a frequency range of 5.5-6.5 Hz and a monophasic, regular shape 3, 4.
- RMTD are closely linked to the drowsy state and can occur at the transition from wakefulness to N2 sleep, as well as during REM periods with interspersed drowsy patterns 3.
- The prevalence of RMTD during N2 sleep has been estimated to be around 1.3% in a study of 1163 consecutive patients 4.
- Network alterations in temporal lobe epilepsy during non-rapid eye movement sleep and wakefulness have been investigated, with findings suggesting that theta activity may play a role in the generation of downstates during N2 sleep 5.
Characteristics of RMTD
- RMTD are characterized by a frequency range of 5.5-6.5 Hz and a monophasic, regular shape 3.
- They are often localized to the mid-temporal region, with occasional spread to anterior or posterior regions 3.
- RMTD can occur bilaterally, simultaneously, or alternately, and are closely linked to the drowsy state 3.
- They can be observed during wakefulness, NREM sleep, and REM sleep, with a higher prevalence during N2 sleep 4.
Relationship to Sleep Stages
- RMTD can occur during the transition from wakefulness to N2 sleep, as well as during REM periods with interspersed drowsy patterns 3.
- They are more pronounced during N2 sleep compared to N3 sleep 2.
- The occurrence of RMTD during N2 sleep may be related to the generation of downstates, which are periods of reduced cortical activity 2.