Twò Anpil neron Piye la Memwa

Too Many Neurons Spoil the Memory

Nouvo rechèch revele fòmil yo selilè pa ki memwa-kodaj rezo nerono sòti


Powered by Guardian.co.ukAtik sa a ki gen tit “Twòp newòn gate memwa a” te ekri pa Mo Costandi, pou theguardian.com nan Vandredi 12yèm fevriye 2016 15.15 UTC

Manyè di m 'ki kote rete panse yo, bliye toutotan ou rele yo soti? Manyè di m 'ki kote rete bonheur yo nan tan lontan, ak ki kote lanmou yo ansyen, Lè yo pral renouvle ankò, ak nwit la la nan oubli sot pase, Pou m 'ka Traverse fwa ak espas lwen aleka, epi pote konfò nan yon lapenn prezan ak yon jou lannwit nan doulè? Ki kote ou prale, O te panse? Nan ki peyi aleka se vòl ou? Si ou returnest nan moman sa a prezan nan mizè, Eske se vre ou pote konfò sou zèl ou, ak dews ak siwo myèl ak renmèd, Ou pwazon soti nan sovaj yo dezè, nan je yo nan envier la?

Nan gade powèm sezon l ', Visions nan pitit fi Albion, William Blake bèl bagay sou nati a nan memwa, kapasite li nan mantalman transpòte nou nan fwa byen lwen ak kote, ak emosyon yo gen anpil pouvwa, pozitif ak negatif alafwa, ki souvenirs nou an ka suscité. gade powèm la gen kesyon ki rete trè enpòtan jodi a, tankou sa k ap pase nan memwa long pèdi nou an, ak ki jan nou rekipere yo?

Plis pase de syèk apre, fòmil yo nan depo memwa ak Rekipere yo ki pi intans etidye fenomèn yo nan syans nan sèvo. Li nan lajman kwè ke fòmasyon memwa enplike nan ranfòse nan koneksyon ki genyen ant fèbleman distribye rezo nan newòn nan yon estrikti nan sèvo rele ipokanp la, e ke Rekipere ki vin apre enplike nan reyaktivasyon an menm formasyon yo nerono. Men,, nerosyantifik toujou lite reponn kesyon Blake a definitivman.

Koulye a,, gen yon ekip chèchè nan University of Geneva te fè yon lòt davans enpòtan nan konpreyansyon nou nan fòmil yo neral kache fòmasyon memwa. Lè l sèvi avèk yon metòd eta-of-atizay la yo rele optogenetics, yo montre ki jan formasyon yo nerono ki programme memwa sòti, revele ke formasyon ki gen twò anpil newòn - oswa twò kèk - afekte Rekipere memwa.

optogenetics se yon teknik trè pwisan ki enplike nan entwodwi pwoteyin alg rele channelrhodopsins (ChRs) nan newòn. Sa a rann selil yo sansib a limyè, sa yo ki gwoup espesifye nan yo ka chanje limen oubyen etenn, lè l sèvi avèk pulsasyon nan limyè lazè lage nan sèvo a atravè fib optik, sou yon peryòd tan nan milisgond.

Nan dènye ane yo, chèchè yo te itilize optogenetics ou mete lejann sou newòn ipokanpal ki vin aktif pandan fòmasyon memwa nan sèvo a sourit, ak yo manipile formasyon yo ki make nan divès fason. Nan fason sa a, yo ka aktive formasyon yo menm pwovoke Rekipere memwa; chanje memwa pè limen oubyen etenn; konvèti memwa negatif nan sa ki pozitif, oswa vis vèrsa; e menm implant antyèman fo memwa nan sèvo yo nan sourit.

Rechèch la nouvo, ki te dirije pa Pablo Mendez ak byen ta nan Dominique Muller nan, ki trajik te mouri nan yon aksidan glisman nan mwa avril ane pase a, baze sou travay nan sa a pi bonè. Yo te kreye manipile jenetikman sourit eksprime kr nan selil granule sou yon bò nan sèvo a, nan dante rejyon nan ipokanp la. selil Machin granule yo newòn yo prensip nan rejyon sa a nan ipokanp la, ki fè yo te panse yo dwe kritik pou fonksyon ipokanpal tankou memwa ak espasyal navigasyon. Yo mete bèt yo nan kaj gwo, sa ki pèmèt kèk nan yo yo eksplore anviwònman nouvo yo. An atandan, yo optogenetically aktive selil granule o aza nan kèk nan sourit yo, men se pa lòt moun.

Ipokanpal selil granule eksprime Channelrhodopsin (nan wouj).
Ipokanpal selil granule eksprime Channelrhodopsin (nan wouj). Imaj: Pablo Mendez

Lè yo diseke ak egzamine sèvo bèt yo ' 45 minit pita, chèchè yo te jwenn espasyal eksplorasyon evoke plotonen aktivite nan formasyon nan newòn ipokanpal, jan yo detèmine pa nivo nan kfo, yon sa yo rele 'imedya byen bonè' jèn ki se chanje sou byen vit lè newòn kòmanse nan dife. Importantly, sourit pèmèt yo eksplore kaj yo te gen pi wo nimewo nan kfo-expressing granule cells than those left in their home cages for the duration of the experiment, and those that received optogenetic stimulation during the exploration had significantly higher numbers of kfo–positive neurons than those that did not.

This showed that spatial exploration evokes activity in ensembles of dentate granule cells, and that randomly altering the activity of these networks with optogenetic stimulation increases the size of the ensembles, or the number of cells within them.

But does manipulating the size of the ensembles have any effect on behaviour? To find out, Mendez and his colleagues placed mice expressing ChR in their hippocampi into another cage, and gave them several mild electric shocks. With repetition of this treatment, the mice quickly learn to fear the cage, and quickly freeze up when returned into it, even when they are not given more shocks.

This time, the researchers optogenetically stimulated random granule cells in some of the mice, men se pa lòt moun, during the training, in order to increase the size of the neuronal ensemble that encodes the fearful memory. These mice exhibited less freezing behaviour when returned to the same cage than others who received no stimulation. But the stimulation also created artificial fear memories, such that the animals froze up in other situations, twò.

Inhibition of random granule cells had the same effect, suggesting that merely altering the number of neurons in the ensemble interfered with the animals’ ability to recall the fearful memories. These findings are consistent with those of an earlier study, which also showed that inhibiting or stimulating granule cell activity impairs contextual learning.

To understand why this might be, the researchers performed another series of experiments, using microelectrodes to record the activity of neurons in slices of hippocampal tissue. These experiments showed that optogenetic stimulation of granule cells produces a robust response in neighbouring interneurons, which release the inhibitory neurotransmitter GABA.

Se konsa, the firing of granule cells leads inhibitory interneurons, which dampen adjacent granule cells and prevent them from entering the ensemble. Nan fason sa a, interneurons appear to stabilize newly-formed memories by regulating the number and distribution of granule cells involved in encoding memories. Activating or silencing random granule cells upsets this process and alters the number of granule cells, which may make the new memories unstable.

“In this study, we used a simple form of memory, the memory of a spatial context, but the challenge is studying how more complex experiences are memorized, and how the brain deals with the storage of multiple experiences,” says Mendez. “Understanding these questions could help us to understand the limits of the brain’s storage capacity.”

Reference

Stefanelli, T., et al. (2016). Hippocampal Somatostatin Interneurons Control the Size of Neuronal Memory Ensembles. newòn, 89: 1-12. DOI: 10.1016/j.neuron.2016.01.024 [Abstract]

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