Biology Reference
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learning and degraded place-cell activity in CA1 (Cho
et al.
, 1998). Importantly these effects
were combined with reduced stimulation-induced long-term plasticity.
4.3. Stimulation-induced modification of place fields
Another interventional strategy to explore place field plasticity is an external plasticity
induction that mimics naturally occurring plasticity patterns.
Figure 5. Place field representation can be modified by LTP-inducing stimulation. A. Example of place
cell with unidirectional change of place field after LTP. Each map represents 10-20 min of
counterclockwise or clockwise runs (curved arrows). Between run sessions the rat was placed back to
the home cage. Low-frequency stimulation (LFS) or tetanic stimulation (HFS) were given. There is a
decline of the initially recorded place field after the HFS protocol and also an emergence of a new place
field during counterclockwise runs. B. The same cell has no significant change in place representation
after LTP, when the animal is moving in a clockwise direction. Besides the unidirectional changed
place fields LTP induction can lead to bidirectional changes as well as no place field changes in both
directions (adapted from (Dragoi
et al.
, 2003)).
Hippocampal place cells are either silent or discharge with single spikes during
behavioural arousal (O'Keefe, 1976). Complex spike bursts are also known to occur (Muller
et al.
, 1987; Gothard
et al.
, 2001) in the time course of the depolarizing theta oscillation due
to the rhythmic decrease of perisomatic inhibition (Kamondi
et al.
, 1998). Consistent with
this event, bursts of spikes significantly increase the effectiveness of synaptic transmission
and at the same time induce frequency-dependent synaptic plasticity
(Csicsvari
et al.
, 1998;
Harris
et al.
, 2001; Hausser
et al.
, 2004). Pairing presynaptic activity with postsynaptic bursts
in hippocampal pyramidal cells in vitro results in LTP of activated synapses (Magee &
Johnston, 1997; Pike
et al.
, 1999). Pairing of presynaptic and postsynaptic activity of
neurons, as modeled by long-term potentiation models, has been suggested to be the possible
mechanism underlying synaptic weight changes in hippocampal network (Levy & Steward,
1979; Magee & Johnston, 1997; Markram
et al.
, 1997).
The effect of LTP as means to
explore the relations between the neurocognitive events underlying spatial representation and
synaptic plasticity (O'Mara, 1995).
Induction of long-term stimulation-evoked EPSP changes
