What hap­pens to your brain dur­ing run­ner’s high?

The Globe and Mail (Alberta Edition) - - NEWS LIFE & ARTS - ALEX HUTCHIN­SON Alex Hutchin­son is the au­thor of En­dure: Mind, Body, and the Cu­ri­ously Elas­tic Lim­its of Hu­man Per­for­mance. Fol­low him on Twit­ter @sweatscience.

Run­ner’s high, in the pop­u­lar imag­i­na­tion, is an en­dor­phine­uphoric in­ter­lude. As neu­ro­sci­en­tist and run­ner Arnold Man­dell fa­mously de­scribed it in the 1970s: “Colours are bright and beau­ti­ful, wa­ter sparkles, clouds breathe, and my body, swim­ming, de­taches from the Earth.”

That sounds won­der­ful – but to most run­ners, it’s false ad­ver­tis­ing. In­stead, the neu­ro­chem­i­cal re­wards of run­ning tend to be sub­tle and highly vari­able, and the causes re­main poorly un­der­stood by sci­en­tists. That com­plex­ity is on full dis­play in a new study that re­veals the po­tent mix of brain chem­i­cals un­leashed by sus­tained ex­er­cise, and ex­plores how our genes in­flu­ence our in­di­vid­ual re­sponses.

The study, which ap­pears in the jour­nal Medicine & Sci­ence in Sports & Ex­er­cise, was led by Penn­syl­va­nia State Univer­sity neu­ro­sci­en­tist and med­i­cal re­searcher Steven Hicks – him­self a for­mer col­le­giate long-dis­tance run­ner – who ap­plied a new tech­nique that en­abled him to look at which sets of genes are turned up or down in the brain dur­ing ex­er­cise.

The most pop­u­lar ex­pla­na­tion for run­ner’s high fin­gers en­dor­phins, the body’s in­ter­nal mor­phine equiv­a­lent, as the cul­prit. But re­cent stud­ies have also im­pli­cated other sets of brain chem­i­cals in­clud­ing en­do­cannabi­noids, the body’s ver­sion of mar­i­juana’s ac­tive in­gre­di­ents, re­sult­ing in sev­eral con­flict­ing the­o­ries about the phe­nom­e­non’s bi­o­log­i­cal un­der­pin­nings.

Hicks’s study of­fered an op­por­tu­nity to pit these the­o­ries against each other by an­a­lyz­ing “mi­croRNAs,” a class of small sig­nalling mol­e­cules dis­cov­ered in the 1990s. These mi­croRNAs reg­u­late how strongly dif­fer­ent genes are ex­pressed in cells through­out your body, in­clud­ing the brain. By an­a­lyz­ing mi­croRNAs in a sim­ple spit test, the re­searchers would get clues about which brain path­ways were most ac­tive dur­ing run­ner’s high.

In 2017, Hicks and his col­leagues pub­lished data sug­gest­ing that mi­croRNA anal­y­sis could be used to di­ag­nose con­cus­sion. To de­velop a prac­ti­cal di­ag­nos­tic test, re­searchers first need to fig­ure out which sig­nals are turned on and off dur­ing ex­er­cise with no con­cus­sion – hence their in­ter­est in run­ners.

As a long-time run­ner, Hicks de­cided to use the op­por­tu­nity (and fund­ing from the com­pany de­vel­op­ing the mi­croRNA con­cus­sion test) to tack on some ad­di­tional anal­y­sis of run­ner’s high.

To do so, he took spit tests from a group of col­le­giate run­ners be­fore and after their weekly long run, which av­er­aged 18 kilo­me­tres. He used ques­tion­naires to de­ter­mine who ex­pe­ri­enced a run­ner’s high, based on cri­te­ria such as im­proved mood, lost sense of time (go­ing at least 30 min­utes dur­ing the run with­out check­ing a watch) and re­port­ing feel­ing “strong,” “ef­fort­less,” “re­laxed” or “eu­phoric.” In to­tal, 13 run­ners met the cri­te­ria, and their re­sults were com­pared with a matched group of 12 run­ners with sim­i­lar char­ac­ter­is­tics who didn’t ex­pe­ri­ence a run­ner’s high.

Of the 2,800 mi­croRNAs that have been iden­ti­fied in hu­mans, six showed sig­nif­i­cant changes in the run­ner’s-high group com­pared with the con­trol group. Sure enough, some were as­so­ci­ated with the opi­oid path­ways that re­spond to en­dor­phins. But, oth­ers were as­so­ci­ated with en­do­cannabi­noid pro­cess­ing, and also with a neu­ro­trans­mit­ter called GABA that plays a role in, among other things, the feel­ing of se­da­tion you get from drugs such as ben­zo­di­azepines. In other words, in the clash of ri­val the­o­ries of run­ner’s high, the an­swer was all of the above and more.

There was an­other telling wrin­kle that con­firmed Hicks’s ques­tion­naire had suc­cess­fully picked out run­ners for whom some­thing spe­cial was hap­pen­ing in the brain. Those clas­si­fied as hav­ing run­ner’s high also ex­pe­ri­enced a clin­i­cally sig­nif­i­cant drop in core tem­per­a­ture and had more di­lated pupils than the con­trol group after the run – both hall­marks of ben­zo­di­azepine use.

Still, they weren’t nec­es­sar­ily bab­bling about breath­ing clouds and their bod­ies de­tach­ing from the Earth. In some ways, what’s most in­ter­est­ing about the find­ings is that they sug­gest run­ner’s high isn’t just one thing and doesn’t have to be ex­treme. “It’s a con­tin­uum, not a yes-no thing,” Hicks says.

So, if you’ve de­cided to make 2019 the year you stick with run­ning, don’t hold out for big eu­phoric in­ter­ludes. In­stead, tune in to the more sub­tle changes in mood and out­look – what run­ning writer Scott Dou­glas calls “the ‘yes’ sen­sa­tion” – that ac­com­pany even the most un­spec­tac­u­lar run. And stop check­ing your watch.

If you’ve de­cided to make 2019 the year you stick with run­ning, don’t hold out for big eu­phoric in­ter­ludes.

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