▁syn apt ic ▁pl astic ity ▁in ▁motor ▁neur ons . ▁Furthermore , ▁when ▁a ▁no x ious ▁stim ulus ▁was ▁ ▁applied ▁to ▁either ▁the ▁head ▁or ▁tail ▁and ▁pa ired ▁with ▁a ▁light ▁touch ▁to ▁the ▁si phon , ▁it ▁produced ▁a ▁strong ▁motor ▁response , ▁called ▁g ill ▁withdraw al ▁ref lex . ▁Ev idence ▁for ▁long - term ▁pl astic ity ▁changes ▁was ▁observed ▁several ▁days ▁later ▁when ▁only ▁a ▁light ▁touch ▁to ▁the ▁si phon ▁el ic ited ▁the ▁same ▁strong ▁response ▁due ▁to ▁a ▁phenomen on ▁called ▁sens it ization . ▁These ▁studies ▁show ▁evidence ▁for ▁heter os yn apt ic ▁strength ening ▁between ▁sens ory ▁and ▁motor ▁neur ons ▁in ▁Ap ly s ia ▁motor ▁circuit ry . ▁ ▁D op am iner g ic ▁syn aps es ▁H eter os yn apt ic ▁pl astic ity ▁is ▁not ▁sole ly ▁restricted ▁to ▁ser ot on in . ▁D op am ine ▁has ▁also ▁been ▁shown ▁to ▁act ▁in ▁a ▁ne uro ▁mod ul atory ▁fashion . ▁Much ▁like ▁the ▁ser ot on in ▁re cept ors ▁in ▁Ap ly s ia , ▁dop am ine ▁re cept ors ▁are ▁G - prote in - cou ple d ▁re cept ors ▁that ▁activ ate ▁c AMP ▁production . ▁This ▁process , ▁however , ▁is ▁important ▁for ▁the ▁storage ▁of ▁mem ories ▁in ▁m amm als , ▁while ▁ser ot on in ' s ▁occurs ▁in ▁in verte br ates . ▁Within ▁dop am iner g ic