BOTH NOVELTY AND OBLIGATORY AUDITORY EVOKED POTENTIALS ARE ABNORMAL IN INFANTS WITH INFANTILE SPASMS

Objectives: Infantile spasms (IS) are associated with severe developmental delay, perhaps related to abnormal temporal lobe function. This study used auditory evoked potentials (AEPs), generated in the temporal lobe, to assess cortical function in infants with IS.

Methods: Thirty-two control infants and thirty infants with IS (1–15 months) were recruited. An oddball paradigm was used with standards (p=80%, 1kHz), deviants (p=10%, 1.5kHz) and brief novel sounds (p=10%), delivered binaurally at 75dB via speakers at 30cm. The endogenous novelty components N2 and P500 were recorded at M1, M2, C3, C4, Cz, P7, P8 and M1, M2, P7, P8 respectively. Obligatory components P150 and P350 were measured at frontal (F3, F4) and central (C3, C4) electrodes after referencing to combined mastoids and low-pass filtering at 10Hz. Recordings were made during wakefulness and sleep (stage II), replicated at least twice.

Results: Reproducible AEP components were recorded in all control infants, showing shortening of P150 and P350 latencies with increasing age (p<0.001). No AEP components could be identified in 50% of infants with IS. When AEPs were visible in IS children, the P150 latency was significantly prolonged compared to controls (p<0.001) during both wakefulness and sleep. The N2 in controls was only affected during wakefulness, while the P500 showed marked shortening with age (p<0.001) irrespective of state of arousal. N2 and P500 were significantly delayed in both states in infants with IS (P<0.001).

Conclusion: Abnormalities of both obligatory and endogenous components suggest that infantile spasms not only interfere with auditory processing at the level of the primary and secondary auditory cortex, but also higher auditory processing in a wider network. These findings must be interpreted in the context of an immature auditory cortex in the first year of life; their clinical implications are being investigated.