{"id":2915,"date":"2015-10-29T05:59:45","date_gmt":"2015-10-29T05:59:45","guid":{"rendered":"http:\/\/www.kurzweilai.net\/?p=265556"},"modified":"2015-10-30T06:52:57","modified_gmt":"2015-10-30T06:52:57","slug":"what-happens-in-the-brain-when-we-learn","status":"publish","type":"post","link":"https:\/\/hoo.central12.com\/fugic\/2015\/10\/29\/what-happens-in-the-brain-when-we-learn\/","title":{"rendered":"What happens in the brain when we learn"},"content":{"rendered":"
\"\"<\/a>

Isolated cells in the visual cortex of a mouse (credit: Alfredo\/Kirkwood (JHU))<\/p><\/div>\n

A Johns Hopkins University<\/a>-led research team has proven a working theory that explains what happens in the brain when we learn, as described in the current issue of the journal\u00a0Neuron<\/em><\/a>.<\/p>\n

More than a century ago, Pavlov figured out that dogs fed after hearing a bell eventually began to salivate when they heard the bell ring. The team looked into the question of how Pavlov\u2019s dogs<\/a> (in “classical conditioning”) managed to associate an action with a delayed reward to create knowledge. For decades, scientists had a working theory of how it happened, but the team is now the first to prove it.<\/p>\n

\u201cIf you\u2019re trying to train a dog to sit, the initial neural stimuli, the command, is gone almost instantly — it lasts as long as the word sit,\u201d said neuroscientist\u00a0Alfredo Kirkwood<\/a>, a professor with the university\u2019s\u00a0Zanvyl Krieger Mind\/Brain Institute<\/a>. \u201cBefore the reward comes, the dog\u2019s brain has already turned to other things. The mystery was, \u2018How does the brain link an action that\u2019s over in a fraction of a second with a reward that doesn\u2019t come until much later?\u2019 \u201d<\/p>\n

Eligibility traces
\n<\/strong><\/p>\n

The working theory — which Kirkwood\u2019s team has now validated\u00a0experimentally — is that invisible \u201csynaptic eligibility traces\u201d effectively tag the synapses activated by the stimuli so that the learning can be cemented with the arrival of a reward. The reward is a neuromodulator<\/a>* (neurochemical) that <\/em>floods the dog\u2019s brain with \u201cgood feelings.\u201d Though the brain has long since processed the “sit” command, eligibility traces in the synapse respond to the neuromodulators, prompting a lasting synaptic change, a.k.a. “learning.”<\/p>\n

The team was able to prove the eligibility-traces theory by isolating cells in the visual cortex of a mouse. When they stimulated the axon of one cell with an electrical impulse, they sparked a response in another cell. By doing this repeatedly, they mimicked the synaptic response between two cells as they process a stimulus and create an eligibility trace.<\/p>\n

When the researchers later flooded the cells with neuromodulators, simulating the arrival of a delayed reward, the response between the cells strengthened (“long-term potentiation”) or weakened (“long-term depression”), showing that the cells had \u201clearned\u201d and were able to do so because of the eligibility trace.<\/p>\n

\u201cThis is the basis of how we learn things through reward,\u201d Kirkwood said, \u201ca fundamental aspect of learning.\u201d<\/p>\n

In addition to a greater understanding of the mechanics of learning, these findings could enhance teaching methods and lead to treatments for cognitive problems, the researchers suggest.<\/p>\n

Scientists at the University of Texas at Houston and the University of California, Davis were also involved in the research, which was supported by grants from JHU’s\u00a0Science of Learning Institute<\/a>\u00a0and National Institutes of Health.<\/p>\n

* The neuromodulators tested were norepinephrine, serotonin, dopamine, and acetylcholine, all of which have been implicated in cortical plasticity (ability to grow and form new connections to other neurons).<\/em><\/p>\n

\n

Abstract of\u00a0Distinct Eligibility Traces for LTP and LTD in Cortical Synapses<\/em><\/strong><\/p>\n

In reward-based learning, synaptic modifications depend on a brief stimulus and a temporally delayed reward, which poses the question of how synaptic activity patterns associate with a delayed reward. A theoretical solution to this so-called distal reward problem has been the notion of activity-generated \u201csynaptic eligibility traces,\u201d silent and transient synaptic tags that can be converted into long-term changes in synaptic strength by reward-linked neuromodulators. Here we report the first experimental demonstration of eligibility traces in cortical synapses. We demonstrate the Hebbian induction of\u00a0distinct traces for LTP and LTD and their subsequent timing-dependent transformation into lasting changes by specific monoaminergic receptors anchored to postsynaptic proteins. Notably, the temporal properties of these transient traces allow stable learning in a recurrent neural network that accurately predicts the timing of the reward, further validating the induction and transformation of eligibility traces for LTP and LTD as a plausible synaptic substrate for reward-based learning.<\/p>\n","protected":false},"excerpt":{"rendered":"

A Johns Hopkins University-led research team has proven a working theory that explains what happens in the brain when we learn, as described in the current issue of the journal Neuron. More than a century ago, Pavlov figured out that dogs fed after hearing a bell eventually began to salivate when they heard the bell ring. […]<\/p>\n","protected":false},"author":13,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[49,43],"tags":[],"class_list":["post-2915","post","type-post","status-publish","format-standard","hentry","category-cognitive-scienceneuroscience","category-news"],"_links":{"self":[{"href":"https:\/\/hoo.central12.com\/fugic\/wp-json\/wp\/v2\/posts\/2915"}],"collection":[{"href":"https:\/\/hoo.central12.com\/fugic\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/hoo.central12.com\/fugic\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/hoo.central12.com\/fugic\/wp-json\/wp\/v2\/users\/13"}],"replies":[{"embeddable":true,"href":"https:\/\/hoo.central12.com\/fugic\/wp-json\/wp\/v2\/comments?post=2915"}],"version-history":[{"count":3,"href":"https:\/\/hoo.central12.com\/fugic\/wp-json\/wp\/v2\/posts\/2915\/revisions"}],"predecessor-version":[{"id":2988,"href":"https:\/\/hoo.central12.com\/fugic\/wp-json\/wp\/v2\/posts\/2915\/revisions\/2988"}],"wp:attachment":[{"href":"https:\/\/hoo.central12.com\/fugic\/wp-json\/wp\/v2\/media?parent=2915"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/hoo.central12.com\/fugic\/wp-json\/wp\/v2\/categories?post=2915"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/hoo.central12.com\/fugic\/wp-json\/wp\/v2\/tags?post=2915"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}