Somatosensory evoked potentials of the normal human neonate in REM sleep, in slow wave sleep and in waking.

TL;DR: The evoked somatosensory potentials in newborns permit a consistent analysis of both "primary" and late components of the cerebral responses and the sleep stages represent one of the major parameters to be considered in their investigation.

About: This article is published in Electroencephalography and Clinical Neurophysiology.The article was published on 1970-08-01 and is currently open access. It has received 112 citations till now. The article focuses on the topics: Sleep Stages & Sleep spindle.

Summary

Stimulatio n and rec o rding

• Each pair of électrodes was con nected, with the cathode proximal, to a constant current stimulator which delivered a square puise of 0.5 msec and 16 mA.
• Fixation of silver dises with adhesive was discarded in favour of very fine stérile stainless steel needles inserted subcutaneously.
• The référence électrodes were placed on the forehead, the ear and the inion.
• When useful the data from différent runs in a given sleep state, recorded in one session, were pooled during the averaging.

Procédure

• The babies were brought to the Unit in the early afternoon.
• After the électrodes had been placed they were bottle-fed and allowed to go undisturbed through their sleep cycles until they woke up some time before the next feed.
• The strength of the finger stimulus was carefully adjusted to be adéquate for evoked potential analysis and yet insufficient to interfère with the natural séquence of sleep states.
• The interval between stimulus was atleastS sec, and in most cases 5-12 sec, in order to avoid interaction between successive responses.
• Besides monitoring the polygraph record on-hne, the baby's face and the bodily and eye movements were closely observed throughout the session, which lasted generally 2 h.

Identification of sleep and waking states

• This study does not deal with evoked potentials recorded during the periods of transition which occurred as the baby went from one stage of sleep to another.
• During the session between two feeds the newborns were sleeping most of the time.
• There were no bodily movements except for occasional jerks.
• The intervais fluctuated more in REMS, as evidenced by the more dispersed histograms (Fig. 9, D, E and 11, D ) and by the larger mean standard déviation.

Nomenclature of evoked response components

• After preliminary tests had elucidated the suitable expérimental conditions, characteristic wave forms were consistently recorded in the thirty-four babies here considered.
• The evoked potentials recorded at the pariétal focus are discussed in terms of the simple nomenclature presented in Fig. 1 .

The positive components Pi and Pz

• Ni at the pariétal focus provides the most consistent feature which distinguishes the two stages of sleep.
• The second positive deflection P2 is always présent in SWS runs.
• When the séparation between Pi and P2 is incomplète, as in Fig. 5 , their respective durations cannot be estimated accurately.
• Fig. 6 compares for the same session 2 REMS in both of which irregular respiration, the small amplitude fast EEG and loss of muscle tone with occasional abrupt bursts are présent.

Comparison with vertex potentials

• The potentials evoked by the same stimulus at the vertex were routinely recorded on FM tape.
• Fig. 9 documents SWS and REMS runs with typical responses at the somatosensory projection in B and E.
• In C, the vertex response in SWS présents two positive components which correspond in time to P2 and P3.
• This différence is not significant (P = 0.6) and it may be proposed that the components with P2 features are related to a common electrogenesis.
• The vertex wave form was thus quite différent from that of the pariétal potential inREMS(Fig. 9, F, G ).

The intervais between stimuli

• Particularly in the SWS runs.
• This procédure minimizes the influence of any trend in the expérimental conditions during sleep stages.
• Comparison of the records in H and / suggests that there is as much variation among the samples at a given interval as between the samples at the two intervais considered.
• It is difficult to detect small significant différences in the wave form at large intervais but it can be said that in SWS the responses do not appear to interact for intervais between stimuli of 15 to 10 sec.
• Intervais of 8 sec appear to be at about the limit and intervais of 4 or 3 sec definitely induce changes in the potentials, especially in their late components.

Age of suhjects

• No significant différences were found in the potentials recorded from newborns on their first and on their sixth days.
• The clinically accepted "newborn" period indeed extends over the first week.

DISCUSSION

• Consistent results were obtained in the thirtyfour newborns because many of the relevant parameters had been identified in preliminary studies.
• This results in a marked increase in the total duration of the initial positivity of the response in SWS (Fig. 4, E ).
• It can be suggested that P2 is generated at a midline région and that this activity increases and expands in SWS.
• In waking the evoked potentials appear rather similar to those in activated REMS (Fig. 7, 8 ).
• The evoked somatosensory potentials in newborns permit a consistent analysis of both "primary" and late components of the cérébral responses and the sleep stages represent one of the major parameters to be considered in their investigation.