EEG and Brain Connectivity: A Tutorial - Bio-Medical Instruments, Inc.

Fig. 22 – Illustration of phase straightening where the change or discontinuity from – 180 0 to +
180 0 is removed by adding or subtracting 360 0 depending on the direction of change (adapted
from Otnes and Enochson, 1972).
Phase straightening is important when computing the first and second
derivatives of the time series of phase differences because the discontinuity
between – 180 0 to + 180 0 can produce artifacts. All of the derivatives and
phase reset measures in this paper were computed after phase straightening
in order to avoid possible artifact.
23 – EEG Spindles and Burst Activity
The human Electroencephalogram is characterized by electrical events
that have a specific shape and physiological origin called “spindles” or
“burst activity”. A spindle is defined as a rhythmic and sequential build up
of EEG amplitudes that wax and wane and appears as an “envelope”
structure. Spindles are also referred to as augmenting and recruiting
responses (Steriade, 1995). Spindles are especially prevalent during late
drowsiness and sleep, however, spindles also occur during waking and
focused attention. In animal studies spindle like responses referred to as