Engrams

Karl Lashley

wanted to know where in brain memories stored

lesioned parts of cortex and effects of lesions on maze performance

engram is distributed and not stored in specific region

Engram

enduring offline physical and/or chemical changes that were elicited by learning and underlie newly formed memory associations

Engram cells

cells that constitute critical cellular components of given engram

activated by learning experience, physically or chemically modified by learning experience, reactivated by subsequent presentation of stimuli present at learning experience

fear conditioning

pair tone with shock

set of engram cells undergo plasticity and allocated to that engram

lesioning engram cells abolishes memory of fear conditioning

Immediate Early Genes

genes that are rapidly and transiently expressed in response to neural activation

associated with neural plasticity (ex. c-Fos and Arc)

c-Fos used to identify engram cells

Optogenetics

reversible lesion

light sensitive protiens (opsins) expressed in specific population of neurons, don’t respond to any chemical but light instead

fast temporal res, implanted optic fiber does damage and possible heating

Tagging an Engram

Virus injected into region

if neuron expresses c-Fos and is off Doxycycline, generates optogenetic protein chennelrhodopsin (ChR2)

Engram complex

entire brain-wide engram supporting a memory that is stored in sets of engram cell ensembles in different brain regions connected via an engram cell pathway