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Before considering
abnormal EEG behaviour and any possible correlation with transitory
cognitive impairment, the normal EEG should first be considered. Binnie
(1981) has argued that the normal EEG is often spikey by nature and
adolescents and children will exhibit positive spikes when drowsy. This
phenomenon does not however have an diagnostic significance in relation
to epilepsy. Binnie has also noted that a phenomenon known as ‘spike
wave phantom’ which exhibits low amplitude, six Hz and is also of no
diagnostic significance with regard to epilepsy.
Benign Epileptiform Transients of Sleep produces short sharp spikes over
temporal regions during sleep with slow waves and is found in forty
percent of normal participants, (White et al 1977). In further research
relating to Benign Epileptiform Transients of Sleep, Westmoreland et al
(1979) noted that in participants with partial epilepsy and Benign
Epileptiform Transients of Sleep, they were unrelated in terms of an
epileptic focus.
Mid temporal Rhythmic Discharge is a phenomenon that exhibits a six Hz
frequency over the temporal regions and appears for minutes at a time
and shows no relationship with arousal or sleep. Lipman & Hughes (1969)
have argued that although this phenomenon is rare, its occurrence is
increased in a number of groups including those suffering from epilepsy.
Gibbs & Gibbs (1952) have argued that the presence of Mid Temporal
Rhythmic Discharge is not reliable in terms of the diagnosis of
epilepsy.
A typical finding in a normal EEG is what is known as a Mu rhythm. The
Mu rhythm usually exhibits an eight to thirteen Hz frequency (in the
alpha range) and is identifiable by its shape that resembles a fence
like waveform. The Mu rhythm can be blocked by intent to move (contralaterally)
a part of the upper body such as the arm or the hand, (Binnie, 1982).
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