Circuit Elements Required for Neural Systems - Brain Theory from a Circuits and Systems Perspective - page 55

(b) If a back propagation arrives at a synaptic receptor or spine that is no longer
active in producing pulses, what happens to the back traveling pulse. (ANS.
It goes to the end of the dendrites and vanishes with no further reflections,
because there is no capacitive load there.)
9. State the effects of a back propagating pulse on the following:

(a) Excitatory neurotransmitters at a receptor (ANS. repels positive ions away
from the excitatory receptor)
(b) Inhibitory neurotransmitters around a dendrite (ANS. helps repels positive
ions away from the dendrite)
(c) Can back propagation ever stop a forward moving pulse? (ANS. Yes,
colliding pulses annihilate)

Boolean Logic

10. Provide a logic schematic to give the following Boolean function: Z 1 ¼ AB +

C + B 0

(HINT: Consider reducing the function to a simpler form

A + B 0 + C)
11. Provide a logic schematic to give the following Boolean function:
Z 2 ¼

Z 1 ¼

(A + B)B 0 + CD (HINT: Consider reducing the function to a sim-
pler form Z 2 ¼ AB 0 + CD)

Dendritic Logic

11. Illustrate the following with sketches of dendrites. (A) If pulses are applied to
the output, predict what might appear at the inputs, (B) If pulses are applied to
one input, predict what might appear at the other inputs.

(a) OR gate (ANS. Back propagating pulses on inputs; back propagating pulses
on other input)
(b) AND gate (ANS. No Pulses on inputs; back propagating pulses on other
input)
(c) XOR gate (ANS. Back propagating pulses on inputs; back propagating
pulses on other input)

12. Comment of the timing of pulses for the following dendritic logic gates:

(a) OR gate (ANS. Pulses may come at random)
(b) AND gate (ANS. Pulses to the inputs must come simultaneously to pass a
signal)
(c) NOT gate using XOR (ANS. Pulses to the inputs must come simulta-
neously to make output be at rest)