October 2008. Neuroscience Journal Club. Experience-dependent plasticity of dendritic spines in the developing rat barrel cortex in vivo Balazs Lendvai*, Edward A. Stern, Brian Chen & Karel Svoboda. Processing of Sensory Informations . BRAIN: what for?. ELABORATION OF STIMULA
ELABORATION OF STIMULA
Where is memory stored?
The substrate of memory is:
dendritic spines – maybe…
How is long-term memory stored?
→ Repeated stimulus leaves a TRACE
→ Nervous track repeatedly crossed can be subjected to LTP
→ Activation of cascade biochemical mechanisms that determine STRUCTURAL MODIFICATIONS of the circuit itself
and memory: LTP and LTD
From Science, 2006
→ Activation/deactivation of synapses
→ Protrusion/retraction of spines/filopodia
Do changes in neuronal structure underlie cortical plasticity?1,2
1. Bailey, C. H. & Kandel, E. R. Annu. Rev. Physiol. 55, 397±426 (1993).
2. Buonomano, D. V. & Merzenich, M. M. Annu. Rev. Neurosci. 21, 149±186 (1998).
In vivo high-resolution imaging of barrel cortex neurons infected with SIN-EGFP (Sindbis virus containing the gene for Enhanced GFP).
Spatial arrangement of the whiskers on the rat’s face : matrix of large hairs represented in these brain areas by a topographically similar matrix of cell rings. (A, B)
Barrels: aggregates of cell rings in layer IV of the cerebral cortex . Barrel cortex: area in the somatosensory cortex (C) where neurons are grouped in barrel- like arrangements, with a hollow center of lesser cell density surrounded by a circle of higher cell density.
IMP: one-to-one relationship between each vibrissa and its corresponding barrel.
→ less filopodia
during (P11-13), before (P8-10), after (P14-16) synaptogenesis (whiskers’ use in exploratory behaviour)
Recordings of membrane potential dynamics of regular spiking neurons in P14±16 rats
Measurement of PSPs amplitudes in response to deflections of single whiskers (SW or PW)
Principal whisker response was smaller than in control animals but the surround was stronger and broader
Sensory deprivation has a profound effect on the TUNING of sensory maps of layer 2/3 pyramidal neurons.
Yes: Sensory deprivation markedly (40%) reduced protrusive motility in deprived regions of the barrel cortex
No: Whisker trimming did NOT change the density, length or shape of spines and filopodia
ELECTROPHYSIOLOGICAL MEASUREMENTS: effects on synaptic ACTIVITY
• LTP can be saturated
• You only have a finite number of synapses
• Your brain is in danger of getting full
• Therefore you need LTD