Rudolf Engel

Appraisal of conceptual age of newborn infants by electroencephalographic methods

The “electroencephalographic age” presents an independent parameter for the estimation of the maturational stage of the newborn infant comparable to the determination of bone age by x-ray. Measurements of photically evoked responses render the electroencephalographic method more objective than visual inspection of the electroencephalogram pattern alone. The method is as harmless as translumination by flashlight and can be carried out in the nursery for premature infants by using transportable instruments.

Maturational changes and abnormalities in the newborn electroencephalogram.

Maturational changes in the neonatal period are documented in electroencephalographic patterns and in measurements of photically evoked responses and their latency period. In premature infants the evoked responses in the occipital area appear with considerably longer latency than seen in normal, full‐term infants. Post‐mature infants tend to have shorter latency periods.

Visual Evoked Responses and IQ Scores at School Age

Visual evoked responses (VERS) were obtained in 119 school‐children, aged seven to eight years. Five latency measurements were related to Bender and Wechsler Intelligence Scores for Children in multiple regression analysis, considering also race and sex. Clearly the latency of the VER peaks did not contribute to a prediction of the IQ scores, nor did sex at this age. Race was present in all significant multiple correlations, but its influence in our sample was significant only for predicting verbal IQ, and not performance IQ. None of the visual evoked responses correlated significantly with psychological measurements alone.

Visual evoked responses at birth, verbal scores at three years, and IQ at four years.

In an attempt to determine whether neonatal evoked response measurements are predictive of subsequent verbal and intellectual abilities, a study was made of the relationship between visual evoked response at birth, three measures of speech and language at three years, and Stanford‐Binet scores at four years. Results from 828 children showed that articulation of initial and final consonants at three years was significantly greater in the children who had shown shorter latencies of evoked potentials in the neonatal period.

The usefulness of electroencephalography in curarized newborns.

Curare and other muscle relaxants are being used with increasing frequency in the management of infants who are mechanically ventilated for severe respiratory distress. Neurological evaluation of these paralyzed newborns is difficult and neonatal convulsions may go unrecognized. The present study includes 5 curarized infants in whom neurological impairment was suspected because of complicated pregnancies and perinatal asphyxia. All showed very abnormal EEGs with ongoing paroxysmal activity in the absence of clinical seizures or a severely depressed record. In two of these infants an improvement in the values of the blood-gases coincided with the administration of diazepam. In curarized infants the electroencephalogram is of importance in the evaluation of the background activity, the detection of convulsive brain activity, and in the management of anticonvulsive therapy.

Mental and Motor Scores at 8 months in Relation to Neonatal Photic Responses

Three physiological neonatal variables have been examined for their relationship to three behavioral 8‐month variables in a group of 433 infants. All nine inter‐age correlations were statistically significant. Among the neonatal variables, the correlations involving photic response latency and gestational age were about the same magnitude for each 8‐month variable and were higher than the correlations involving birthweight. At 8 months, the mental test score had higher correlations with the neonatal measures than the fine motor or gross motor scores.

ELECTROENCEPHALOGRAPHIC RESPONSES TO PHOTIC STIMULATION, AND THEIR CORRELATION WITH MATURATION *

Electroencephalographic patterns, awake and asleep, undergo changes with maturation. By analogy to radiological “bone age,” the term “electroencephalographic age” has been coined by Dreyfus-Brisac.’ Testing and measurement of functional performance yield an additional parameter for the evaluation of the electroencephalographic age. The present study was undertaken to further evaluate the relation of electroencephalographic latency measurements to the conceptual age of newborn infants.2 It is relatively easy to discover the responses that occur, usually, though not invariably, after photic stimulation in the projection area of the visual cortex of one or both hemispheres. The response is not limited to a single action potential, but rather i t appears as a sequence of electrical events with positive and negative wave forms following the application of the stimulus. It can be seen again on repeated stimulation if the interval between individual stimuli is not unduly short ( EllingsonY) . In determining the latency interval, Ellingson* measured the distance from the peak of the signal artifact to the peak of the response. We measured the latency from the first deviation from the baseline caused by the signal to the first deviation from the background activity caused by the response sequence. Often, multiple stimulations had to be given before an adequate take-off point from the background activity could be measured and be confirmed by additional well-distinguished take-offs with identical response configurations. The basic test involves the exposure to a single flash (FIGURE 1). The amplitude of the response in this case reached over 100 pv. Repetitive stimulation one second apart often caused a response each time. If more than three flashes per second are offered during the newborn period there are seldom more than one o r two responses seen on visual inspection. In older infants (FIGURE 2 ) a rhythmic wave-train can be produced in the occipital area with the same frequency or harmonics as used for the photic stimulation. This “following the light” is frequently called “photic driving.’’ Repetitive stimulation with frequencies higher than the receptor organ can follow may show an on and off response.

96 Variation in Evoked Response Activity Among Negro, Caucasian and Oriental Neonates of Both Sexes

442 Negro and 108 Oriental neonates were tested in their electroencephalographic response to light and compared with observations on 1507 Caucasian neonates. The latency measured from the stimulus to the onset of the evoked potential is inversely proportional to conceptional age (r = 0.608). This is evident in both sexes and the three races tested, in single as well as multiple births. The males, however, reacted significantly slower than females of comparable conceptional ages. Negroes tend to have shorter latency periods and Oriental longer latencies than Caucasians in both sex groups. Twins and many prematurely born single neonates may show a delay of response activity by the time they reach the estimated date of confinement, but body weight is not the determining factor. In a group of 126 paired twins the first born did not show a significant difference from the behavior of the second twin. The heavier neonate tended to remain the heavier twin, but the mean photic latency followed the slope of the regression line according to conceptional age for both twins. Male and female twins and triplets show a similar sexual difference in latency measurements as found in single births. (APS)