“The neu­rons have a com­pletely dif­fer­ent ac­tiv­ity pat­tern be­fore the move­ment”

Planned and im­me­di­ate move­ments are pro­cessed dif­fer­ently by the brain. Dr Ben­jamin Dann of the Ger­man Pri­mate Cen­ter ex­plains how it might help hu­mans

Focus-Science and Technology - - DISCOVERIES -

What’s the dif­fer­ence be­tween planned move­ments and im­me­di­ate reactions?

One ex­am­ple is when you’re wait­ing for a green light, pre­par­ing to press the gas pedal of your car, but if a child runs onto the street, you have to brake. Both are the same move­ment of putting your foot down, but in one case you have to re­act as quickly as pos­si­ble, in the other you have time to pre­pare.

How did you com­pare the two move­ments?

We used the ex­am­ple of grasp move­ment. This study was done with macaque mon­keys, which are the best model for hu­mans. We trained two mon­keys to grasp a han­dle in front of them with ei­ther a pre­ci­sion grip, like when you pick up a bis­cuit, or a whole-hand or power grip, like when hold­ing a ten­nis rac­quet. On a mon­i­tor, we gave a vis­ual cue which told the mon­key how to grasp. The vis­ual cues were cir­cles: grey for pre­ci­sion grip, green for power grip. There was also a red cir­cle for telling the mon­key not to grip – they were only al­lowed to ex­e­cute the grip once the red cir­cle had dis­ap­peared. The re­searchers showed those cir­cles at var­i­ous 0.1-sec­ond in­ter­vals from 0 to 1.3 sec­onds. In the brain, the first de­ci­sion was to choose the type of grip – power or pre­ci­sion – then wait for the vis­ual cue [the red cir­cle dis­ap­pear­ing] to in­di­cate the start of the move­ment.

And how did you mea­sure brain ac­tiv­ity?

We first im­planted mi­cro­elec­trodes in­side the skull. Un­for­tu­nately any non-in­va­sive method is not suit­able yet as the sig­nal is too blurry. We were able to not just record in­di­vid­ual neu­rons

[ brain cells], but hun­dreds of them – the whole net­work, ac­tu­ally – ev­ery­thing that’s par­tic­i­pated in the plan­ning, as well as in con­trol of the move­ment it­self.

How does the brain ac­tiv­ity dif­fer?

The move­ment it­self is iden­ti­cally coded in the rel­e­vant mo­tor ar­eas of the cor­tex [the brain’s folded outer lay­ers]. How­ever, the pop­u­la­tion of neu­rons in­volved in this process has a com­pletely dif­fer­ent ac­tiv­ity pat­tern be­fore the move­ment is ac­tu­ally ini­tialised. This dis­tinct ac­tiv­ity pat­tern within the brain, or ‘state’, is only present for work­ing mem­ory – short-term mem­ory used while plan­ning move­ments – and not when you re­act right away. All of a sud­den this ex­tra state ap­pears

ABOVE: Ac­cord­ing to a study us­ing macaques, planned and im­me­di­ate move­ments have dis­tinct pat­terns in the brain be­fore the move­ment is ini­tialised

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