Sleep is an important function of the human brain. Sleep and sleep cycles are
fundamental for sensory system development in the whole life cycle of an individual,
including embryonic life, to preserve brain activity, to create long-term
memory, and for learning.
The measurement of brain signals is useful to quantify different brain states, such
as sleep and wake states. The origin of cycles of sleep and wake in higher vertebrate
animals (birds and mammals) are currently unknown, thus it is of particular interest to
combine information that reflects different aspects of brain function.
Our research has been focused on the study of neurological signals during embryonic
life. In this thesis, chicken embryos have been chosen as animal models for many
practical reasons: the ease of access to chicken embryos, the fact that early stages of
development and sleep in chicken are similar to those of humans.
The developed system consists of a transmitter placed outside the eggshell and of a
receiver located outside the incubator. The transmitter and the eggshell are kept inside
the incubator in order to guarantee the survival of the embryo. The communication
between the transmitter and the receiver is implemented via infrared signals.
Subsequently, to improve the insertion and adhesion at the brain-electrode interface,
new flexible polyimide electrodes have been developed instead of the metal wires,
which are commonly used to detect neurological signals. Specifically, two different
types of electrodes have been developed: passive and active. The passive electrode is
based on a conducting polymer (PEDOT:PSS) deposited on a flexible polyimide substrate,
where gold has been used to define the conducting line and the pad contact area.
The active electrode is based on the fabrication of an organic electrochemical transistor
(OECT), for which source and drain electrodes have been made with gold, the channel
has been made with a conducting polymer (PEDOT:PSS) and the gate has been made
with metal. The deposition of PEDOT:PSS has been performed using the inkjet printing
technology. Different types of ink, based on a PEDOT:PSS aqueous solution, have
been tested and electrically characterized.
Finally, in-vivo tests on chicken embryos, using standard metal electrodes, have been
completed to check the performance of the developed EEG system
