Which of the following are examples of modulatory signaling, different from 'point-to-point' signaling?
(select all that apply)

a. A retinal ganglion neuron synapsing onto a few neurons in the thalamus
b. The inputs that give simple cells of V1 their orientation tuning
c. Hormones released into the blood stream
d. Norepinephrine neurons releasing neurotransmitter onto >10k neurons across the cortex