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iPlant
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Monoamines and the reward system The human brain weighs about 1.4 kg and consists of blood vessels (~20% of volume), supporting glial cells, and some 100 billion neurons. A subset of these neurons, called the reward system, monitor value in the environment and in the state of the brain, and generate what we call desire, motivation and volontary movement, as well as attention and learning. Destroying these cells or blocking their activity eliminates learning and the pursuit of rewards in animals. All natural and learned rewards and addictive drugs increase activity in the reward system. Constant, weak, high-frequency deep brain stimulation of the reward system is EC marked in the EU and FDA approved in the US as a treatment for psychiatric conditions. Brief, strong, low-frequency electrical stimulation is the basis of rewarding brain stimulation in animals and the proposed basis of iPlants for human use (see iPlant programming). This section of the site describes the reward system in more detail. 
Dopamine and the frontal lobes, What is dopamine? Riding a bike,
Thoughts on forks, Brainbeat,
The interpretation of dreams, Work in progress
Anatomy of the reward system  At the core of the reward system are dopamine-producing neurons (~400.000
in the primate) located in two brain regions called the ventral tegmental area
and substantia nigra in the midbrain. These neurons extend axons, via the
medial forebrain bundle, into the frontal cortex, striatum, hippocampus
and amygdala, where they release dopamine, which activates D2- and, at
high concentrations, D1-receptors that change the behaviour of target neurons. The dopamine cells themselves recieve input from many
parts of the brain, including their forebrain targets. The nature of
this input determines what the animal finds naturally rewarding. Other
monoamine neurotransmitters with cell bodies in the midbrain and
brainstem, such as serotonin and noradrenaline, also have important
roles to play in reward.Another, cosely related, core of the reward system is the nucleus accumbens in the ventral striatum, which receives denser dopaminergic projections than any other brain region, and is strongly activated in all reward process. Constant, weak, high-frequency deep brain stimulation to the nucleus accumbens is an FDA and EC approved treatment for obsessive compulsive disorder and is currently in trials for other psychiatric disorders including depression and eating disorders. Rewarding brain stimulation could be induced by these implants through switching to a brief, strong, low-frequency current, which, if made conditional, could be used to help motivate people to perform beneficial but difficult behaviours (see iPlant programming). Slow dopamine: attention and motivation Tonic (i.e. long-term) dopamine concentrations in the brain determine our level of attention. This relationship has an inverted U shape: too much dopamine leads to rigid, inflexible thinking, whereas too little leads to distractibility (Cools & Robbins, 2004). Dopamine-producing neurons continuously fire action potentials at a rate of 2-3 Hz. This rate determines the tonic concentration of dopamine in target brain regions (e.g. 5-10 nM in striatum). Broadly speaking, tonic dopamine concentrations determine the signal-to-noise ratio of neuronal activity by reinforcing strongly active groups of neurons and eliminating weakly active ones (Gruber et al 2006). Stimulants such as Adderall, Ritalin and coffee enhance attention by increasing dopamine concentrations, and are particularly in attention deficit disorders since these involve impaired dopamine signalling. In animals, tonic dopamine concentrations rise by 20-100% in novel environments and in anticipation of, or on delivery of, rewards like liquid, food, drugs or sex, and in response to some aversive events (Schultz 2007). About a quarter of all dopamine-producing neurons also steadily increase their firing rate to about twice the baseline rate, for several seconds, in anticipation of uncertain rewards.  Check out the
dopamine fan page on FacebookFast dopamine: reinforcement learning Dopamine neurons fire bursts of 3-4 action potentials at 10-50 Hz in response to unexpected rewards or events that predict a reward. These bursts temporarily raise dopamine concentrations in target brain regions to >100 nM, which activates D1 receptors that allow the streghtening of, and formation of new memories and behavioural habits (Schultz 2007). Although there is some dispute, this is generally considered the basis of reward learning in the brain. Bursts of dopamine may also occur spontaneously, in response to intense stimuli and, in a small number of dopamine neurons projecting to the cortex, in response to aversive events although most dopamine neurons respond to aversive events, including omitted rewards, by transiently reducing their firing rates. Rewarding brain stimulation produces very large increases in dopamine concentrations. Noradrenaline In writing... Noradrenaline is produced by neurons in the locus coeruleus in the brainstem. Projects widely. The structure and synthesis of noradrenaline are closely related to those of dopamine. Noradrenaline appears to be involved in arousal. See Sara 2009 for an overview. Serotonin In writing... Serotonin is produced by neurons in the raphe nuclei in the brainstem. Projects widely. Serotonin appears to be involved in many aspects of affective cognition but is not well understood (Dayan & Huys, 2009). Serotonin depletion in the frontal cortex leads to problems re-evaluating learned patterns of behaviour (Clarke et al 2005). Impaired serotonin function is associated with mood disorders like anxiety, depression, obsessive compulsive disorder, anorexia and bulimia (Lechin et al 2006, Jans et al 2007). Many pharmacological treatments of these disorders (e.g. Prozac, Citalopram) increase baseline serotonin concentrations in the brain. |
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New questions about the iPlant (February 2010) At the International Neuromodulation Conference in Seoul (September 2009) Does secularism fuck you up? (pt.2, pt.3) (June 2009) What we need to accelerate biomedical research and fight aging (May 2009) I can has freedom and dignity? (April 2009) Using Medtronic's Reclaim implant to generate artificial motivation (March 2009) Wired-article-induced neuroscience rant (March 2009) Riding a bike (December 2008) How compliant do we want our children to be? (December 2008) Thoughts on forks (December 2008) Aging (November 2008) Brainbeat (October 2008) |
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What the blogs say |
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The iPlant: Making life easier for the lazy?
(June 2009)
Enogamez iPlant (June 2009) Something Awesome iPlant Brain Implant Advocated for Self-Improvement (June 2009) Technovelgy iPlant - the motivational implant (June 2009) Futurismic A prosthetic motivational system (April 2009) Emerging Ideas Self-determination for the 21st century (April 2009) psique The iPlant (May 2008) Brain Stimulant |
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