Wisq Ħafna Newroni Spoil l-Memorja

Too Many Neurons Spoil the Memory

Riċerka ġdida turi l-mekkaniżmi ċellulari permezz tagħhom in-netwerks newronali kodifikazzjoni memorja jitfaċċaw


Powered by Guardian.co.ukDan l-artiklu intitolat “Wisq newroni jħassru l-memorja” ġie miktub minn Mo Costandi, għall theguardian.com nhar il-Ġimgħa 12 Frar 2016 15.15 UTC

Tell me fejn nitkellem l-ħsibijiet, minsija till thou jsejħulhom raba? Tell me fejn nitkellem l-gost ta 'qodma, u fejn l-tant iħobb qedem, U meta se jkunu ġġedded mill-ġdid, u l-lejl tal-passat oblivion, Dik I tista travers ħinijiet u spazji ferm remota, u jġibu Comforts fi niket preżenti u lejl ta 'uġigħ? Fejn goest thou, ħsieb O? Sa liema art bogħod huwa titjira jsw? Jekk thou returnest sal-mument preżenti ta 'affliction, Jidbiel thou iġibu comforts mal-linji jsw, u dews u l-għasel u balzmu, Jew velenu mill-wilds deżert, mill-għajnejn ta 'l-envier?

Fil poeżija epika tiegħu, Viżjonijiet ta 'l-Ulied il Albion, William Blake jistaqsi dwar in-natura tal-memorja, kapaċità tagħha li mentalment trasport lilna biex ħinijiet bogħod u postijiet, u l-emozzjonijiet qawwija, kemm pożittivi u negattivi, li tifkiriet tagħna jistgħu joħolqu. Il-poeżija fih mistoqsijiet li jibqgħu ferm pertinenti llum, bħal dak li jiġri għall-memorji tagħna fit-mitlufa, u kif nistgħu irkuprata minnhom?

Aktar minn żewġ sekli wara, il-mekkaniżmi ta 'ħżin tal-memorja u l-irkupru huma l-fenomeni aktar intensiv studjat fix-xjenzi tal-moħħ. Huwa maħsub b'mod wiesa li l-formazzjoni memorja tinvolvi t-tisħiħ tal-konnessjonijiet bejn in-netwerks mqassma ftit li xejn ta 'newroni fi struttura moħħ imsejjaħ il-hippocampus, u li l-irkupru sussegwenti jinvolvi riattivazzjoni ta 'l-istess settijiet newronali. u madankollu, newroxjentisti għadhom jissieltu biex twieġeb mistoqsijiet Blake definittivament.

Issa, tim ta 'riċerkaturi fl-Università ta' Ġinevra għamlu avvanz importanti ieħor fil-fehim tagħna tal-mekkaniżmi newrali bażiċi formazzjoni memorja. Permezz ta 'state-of-the-art metodu msejjaħ optogenetics, dawn juru kif il-ensembles newronali li jikkodifikaw memorji jitfaċċaw, tiżvela li ensembles fihom wisq newroni - jew ftit wisq - jfixklux irkupru tal-memorja.

optogenetics huwa teknika estremament qawwija li tinvolvi l-introduzzjoni ta 'proteini alka msejħa channelrhodopsins (ChRs) fis newroni. Dan jirrendi l-ċelluli sensittivi għad-dawl, tali li l-gruppi speċifikati minnhom jistgħu jinxtegħlu jew jintfew, jużaw impulsi ta 'dawl laser mogħtija fil-moħħ permezz fibri ottiċi, fuq skala ta 'żmien ta' millisekondi.

Fis-snin riċenti, riċerkaturi użaw optogenetics li tikketta newroni hippocampal li jsiru attivi waqt il-formazzjoni memorja fil-moħħ ġurdien, u biex jimmanipulaw l ensembles ttikkettjati fil-modi varji. B'dan il-mod, huma jistgħu jattiva l-istess ensembles għall jinduċu irkupru memorja; jaqilbu memorji beżgħana fuq jew barra; jikkonvertu memorji negattivi fis dawk pożittivi, jew viċe versa; u anke impjant memorji għal kollox foloz fil-imħuħ ta 'ġrieden.

Ir-riċerka l-ġdida, immexxija minn Pablo Mendez u l Dominique Muller tard, li traġikament miet fl-inċident gliding f'April tas-sena l, jibni fuq din il-ħidma li saret qabel. Huma ħolqu ġrieden inġinerija ġenetika li jesprimu CHR f'ċelloli granuli fuq naħa waħda tal-moħħ, ġol reġjun dentate tal-hippocampus. ċelloli granuli huma l-newroni prinċipju f'dan ir-reġjun tal-hippocampus, li huma maħsuba li jkunu kritiċi għall-funzjonijiet hippocampal bħal memorja u n-navigazzjoni spazjali. Huma poġġew l-annimali għall-gaġeġ kbar, tippermetti xi wħud minnhom biex jesploraw ambjent ġdid tagħhom. Sadanittant, dawn optogenetically attivati ​​ċelloli granuli każwali f'xi wħud mill-ġrieden, imma mhux oħrajn.

ċelluli granuli hippocampal li jesprimu Channelrhodopsin (bl-aħmar).
ċelluli granuli hippocampal li jesprimu Channelrhodopsin (bl-aħmar). Image: Pablo Mendez

Meta mifrudin u eżaminati imħuħ tal-annimali 45 minuti wara, ir-riċerkaturi sabu esplorazzjoni attività spazjali evokat fil ensembles ta newroni hippocampal, kif determinat mill-livelli ta ' CFOs, ġene "kmieni immedjat" hekk imsejħa li hu mixgħul malajr meta newroni jibdew nar. importanti, ġrieden permessi biex tesplora gaġeġ tagħhom kellhom numri akbar ta ' CFOs-jesprimu ċelloli granuli minn dawk li baqgħu fil-gaġeġ dar tagħhom għat-tul tal-esperiment, and those that received optogenetic stimulation during the exploration had significantly higher numbers of CFOs–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, imma mhux oħrajn, 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, wisq.

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.

għalhekk, the firing of granule cells leads inhibitory interneurons, which dampen adjacent granule cells and prevent them from entering the ensemble. B'dan il-mod, 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. neuron, 89: 1-12. DOI: 10.1016/j.neuron.2016.01.024 [Abstract]

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