Please enable JavaScript.
Coggle requires JavaScript to display documents.
Intracranial Self-Stimulation and the Pleasure Centers of the Brain, : -…
Intracranial Self-Stimulation and the Pleasure Centers of the Brain
Introduction
Intracranial Self Stimulation
Rats, humans, and many other species administer brief bursts of weak electrical stimulation
To specific sites in their own brains
Discovered by Olds and Milner (1954)
Pleasure centers:
Brain sites capable of mediating the phenomenon
Specific brain sites that mediate self-stimulation
Those that normally mediate the pleasurable effects of natural rewards (i.e., food, water, and sex).
Fundamental Characteristics of Intracranial Self-Stimulation
Early studies:
Involved septal or lateral hypothalamic stimulation
Rates of self-stimulation from these sites are spectacularly high
Rats typically press a lever thousands of times per hour for stimulation of these sites
Stopping only when they become exhausted.
Initially assumed to be unitary phenomenon
Its fundamental properties were the same regardless of the site of stimulation.
Findings
lever pressing for brain stimulation was fundamentally different from lever pressing for natural reinforcers (food or water.)
Two puzzling observations:
Many rats stopped pressing the lever almost immediately when the current delivery mechanism was shut off.
Experienced self-stimulators often did not recommence lever pressing when they were returned to the apparatus
After being briefly removed from it.
Rats had to be primed to get them going again
The experimenter simply pressed the lever a couple of times, to deliver a few free stimulations
Circuits mediating intracranial self-stimulation could be natural reward circuits.
Three Studies:
1.Brain stimulation through electrodes that mediate self-stimulation
often elicits a natural motivated behavior
Eating, drinking, or copulation in presence of appropriate goal object.
Producing increases in natural motivation
By food or water deprivation, by hormone injections, or by the presence of prey objects
Often increases self-stimulation rates.
Situations with rewarding effects of brain stimulation and those of natural rewards are almost same.
Rats Lever Pressing for food
Rats Lever Pressing for Brain Stimulation
Mesotelencephalic Dopamine System Intracranial Self-Stimulation
Mesotelencephalic dopamine system
System of dopaminergic neurons
that 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:
some regions of the prefrontal neocortex
limbic cortex
Olfactory tubercle
Amygdala
Septum
Dorsal striatum
Nucleus accumbens (nucleus of the ventral striatum)
Pathways of the system
Nigrostriatal pathway
Network of the axons of dopaminergic neurons that have their cell bodies in the substantia nigra
and project to the dorsal striatum
Degeneration in this pathway is associated with Parkinson’s disease.
Mesocorticolimbic pathway
Network of axons of dopaminergic neurons that have their cell bodies in the ventral tegmental area
And project to various cortical and limbic sites
Plays a role in mediating intracranial self-stimulation.
Evidence:
Many of the brain sites at which self-stimulation occurs are part of the mesotelencephalic dopamine system
Intracranial self-stimulation is associated with increase in dopamine release in the mesocorticolimbic pathway
Dopamine agonists increase intracranial self-stimulation, and dopamine antagonists decrease it
Lesions of this pathway tend to disrupt intracranial self-stimulation.
: