Morphology provides the major means to differentiate needle spikes from interictal epileptiform discharges (IEDs). The waveform differences are most prominent in early childhood, when needle spikes are sharper than IEDs, and during late adolescence, when they oft38463cdd449a328b17adef433fcb6523e333153e8e66493942b4aa066ffe16fd0b260c8c0b11df}/ID(RU3-19)” title=”Cohen, 1969″ onmouseover=”window.status=this.title; return true;” onmouseout=”window.status=”; return true;”>Cohen, 1969; Cohen et al., 1961). Furthermore, needle spikes may occur when some visual function is intact, so the term blindness is also not always accurate (Jeavons, 1964).

Needle spikes may be present at ages as early as about 10 months, but they typically have low amplitude and are very brief until an age of about 2.5 years (Kellaway et al., 1955). By mid-childhood, the spike duration has increased and an after-going slow wave may occur. After-going slow waves are most likely to occur in late childhood, and they then occur less often in adolescence. During adolescence, the spikes become lower in amplitude and briefer in duration, and they may cease to occur at around the end of adolescence (Robertson et al., 1986). Occipital slowing also is more likely to be present, but this is not always the situation and the slowing may not occur at the same time as the needle spikes. Moreover, the slowing may be moreoccur individually or in bursts of several waves (Catani, 1978). Their maximum amplitude varies widely and usually is between 50 and 250 μV. Therefore, they sometimes do not exceed the amplitude of the background activity.