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Intracranial Self-Stimulation and the Pleasure Centers of the Brain,…
Intracranial Self-Stimulation and the Pleasure
Centers of the Brain
Intracranial Self Stimulation
Rats, humans, and other species administer brief
bursts of weak electrical stimulation- specific sites in their own brains
Discovered by Olds and Milner (1954)
Specific brain sites
Those that normally mediate the pleasurable effects of
natural rewards (i.e., food, water, and sex)
Fundamental Characteristics
Initially assumed to be unitary phenomenon
Fundamental properties- same regardless
of site of stimulation
Early studies
Involved septal or lateral hypothalamic stimulation
Rates of self-stimulation from these sites-
spectacularly high
Rats- press- lever thousands of times per hour for
stimulation of these sites
Stopping only when they become exhausted
Findings
lever pressing for brain stimulation was fundamentally
different from lever pressing for natural reinforcers
Two puzzling observations
Many rats stopped- pressing lever- immediately
when the current delivery mechanism- shut off
Experienced self-stimulators- did not recommence
lever pressing when they were returned to the apparatus
Circuits mediating intracranial self-stimulation could be
natural reward circuits
Three Studies
Brain stimulation through electrodes that mediate
self-stimulation
Elicits a natural motivated behavior
Eating, drinking, or copulation in presence of appropriate
goal object
Situations with rewarding effects of brain stimulation
and those of natural rewards- almost same
Rats Lever Pressing
for food
for Brain Stimulation
Producing increases in natural motivation
By food or water deprivation, by hormone injections, or by
the presence of prey objects
Increases self-stimulation rates
Pleasure centers
Brain sites capable of mediating the phenomenon
Meso-telencephalic Dopamine System and
Intracranial Self-Stimulation
Mesotelencephalic dopamine system
System of dopaminergic neurons- projects from the mesencephalon (the midbrain)- into various regions of the telencephalon
These neurons have their cell bodies in two midbrain nuclei
Substantia nigra
Ventral tegmental area
Their axons project to a variety of telencephalic sites
Regions of the prefrontal neocortex
Olfactory tubercle
Amygdala
Limbic cortex
Septum
Dorsal striatum
Nucleus accumbens
2 pathways of the system
Nigrostriatal pathway
Network of the axons of dopaminergic neurons that
have their cell bodies in- substantia nigra
And project to the dorsal striatum
Degeneration in this pathway- associated with
Parkinson’s disease
Mesocorticolimbic pathway
Network of axons of dopaminergic neurons that have
their cell bodies in- ventral tegmental area
And project to various cortical and limbic sites
Plays role in mediating intracranial
self-stimulation
Evidence
Many brain sites at which self-stimulation occurs are part of- mesotelencephalic dopamine system
Intracranial self-stimulation- associated with increase
in dopamine release in- mesocorticolimbic pathway
Dopamine agonists increase intracranial
self-stimulation, and dopamine antagonists decrease it
Lesions of this pathway- disrupt intracranial
self-stimulation
