Place Cells •  Place cell ac)vity codes for more than space •  Rats were trained on a spa)al alterna)on task in t-­‐maze (Wood et al, 2000) •  The ac)vity of pyramidal cells of CA1 field were recorded •  Different cells fired when rats were at different parts of the maze •  2/3 of the cells fired differen)ally in the stem of the T maze on leI-­‐turn and right-­‐turn trials, thus coded for where the animal was going to turn in that trial aIer it got to the choice point •  Thus, pyramidal cells encode both the current loca)on and the intended des)na)on Min 8:49 Demonstra)on Hippocampal Forma)on & Memory Consolida)on Frankland & Bontempi, 2005 Hippocampal Forma)on & Memory Consolida)on •  Bontempi et al (1999) tested mice in a spa)al learning task •  They then tested regional brain ac)va)on while tes)ng the animals’ memory •  The hippocampal ac)vity was higher and posi)vely correlated with performance •  At 25 days, the hippocampal ac)vity was down by 15-­‐20%, the correla)on with the performance was gone •  While the animals were being tested, the ac)vity of several regions of cerebral cortex was elevated instead Hippocampal Forma)on & Memory Consolida)on 5 day group 25 day group Bontempi et al (1999) Hippocampal Forma)on & Memory Consolida)on Bontempi et al (1999) Hippocampal Forma)on & Memory Consolida)on Bontempi et al (1999) Hippocampal Forma)on, Memory Consolida)on, Cor)cal Synap)c Plas)city Normal Deficient Frankland & Bontempi, 2005 Hippocampal Forma)on, Memory Consolida)on, Cor)cal Synap)c Plas)city Frankland & Bontempi, 2005 Hippocampal Forma)on & Memory Consolida)on •  Maviel et al (2004) trained mice in Morris water maze and were tested for their memory •  If hippocampus was deac)vated by admin of lidocaine 1 day aIer the training, mice did not exhibit memory •  Deac)va)on of hippocampus aIer 30 days did not disrupt the performance •  Deac)va)on of several regions of cerebral cortex aIer 30 days impaired memory retrieval memory, but it did not if deac)va)on was 1 day aIer training •  These findings suggest that hippocampus is required for newly formed memories but not for informa9on learned 30 days before, cerebral cortex takes on a role for memory retrieval during this period. Hippocampal Forma)on & Memory Consolida)on Frankland & Bontempi, 2005 Reconsolida)on of Memories Reconsolida)on of Memories •  Memories are altered and get connected to newer memories. The process that involves the modifica9on of long-­‐term memories is called reconsolida9on. •  Electroconvulsive shock causes seizures and erase short-­‐term memory present at the )me and thus prevent consolida)on of these memories •  Misanin et al (1968) showed that long-­‐term memories which are not vulnerable to disrup)on of ECS, can become vulnerable if the original learning experience was first presented. Reconsolida)on of Memories •  If ECS was given right aIer the learning experience, consolida)on was interfered •  If the ECS was given a day later, there was no effect since the memory was already consolidated •  If animals were presented with a reminder s)mulus and thus the memory was reac)vated, ECS treatment right aIer the reminder erased the task memory Reconsolida)on of Memories •  Reconsolida)on appears to require LTP •  Ben Mamou et al (2006) showed that blocking protein synthesis (by anisomycin) interferes with memory consolida)on •  But , it disrupts the memory of a previously learned avoidance task only if a reminder s)mulus is presented •  If an NMDA receptor antagonist is infused to amygdala first, anisomycin did not have an effect even aIer a reminder s)mulus is presented •  Thus, preven)on of synap)c plas)city (LTP) abolishes reconsolida)on •  Similar results were gathered from contextual fear condi)oning and by infusion of anisomycin in hippocampus (Debiec et al, 2002) Reconsolida)on of Memories •  Nader, Schafe, leDoux (2000) Baseline Omiced the CS before anisomycin infusion Reconsolida)on of Memories Nader & Hardt, 2009 Reconsolida)on of Memories Role of LTP in Memory •  As rats learned a maze, the strength of the popula)on EPSP in CA3 field increased, which points at LTP (Mitsuno et al, 1994) •  McHugh et al and Tsien et al (1996) developed muta)ons of gene responsible for the produc)on of NMDA receptors in the CA1 pyramidal cells – thus NMDA receptors did not develop here •  This prevented LTP in mutant mice. The spa)al recep)ve fields of CA1 cells were larger and less focused in these mice •  Mutant animals also exhibited learning deficits: They learned the Morris water maze at a much slower rate than the normal mice. Role of Hippocampal Neurogenesis in Consolida)on • 
Neurons can be produced in the hippocampus of the adult brain, they migrate into the dentate gyrus and extend axons along the mossy fiber tract (they form synapses with other cells of dentate gyrus and CA3 field). • 
Gould et al (1999) trained in Morris water maze either in rela)onal learning condi)on or s)mulus-­‐response learning condi)on • 
Rela)onal learning condi)on doubled the number of new born cells in hippocampus where as the s)mulus-­‐response learning had no effect • 
Jesberger et al (2003) also detected fos protein in newly formed dentate gyrus neurons aIer rela)onal Morris water maze training sugges)ng that these neurons par)cipated in learning. • 
Schmidt-­‐Hieber et al (2004) showed that associa)ve LTP was easier to establish in new born cells sugges)ng their par)cipa)on in the forma)on of new memories. Demonstra)on