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Mechanisms of persistent neuronal activity that may contribute to working memory. When a monkey performs a working memory task neurons in
prefrontal cortex fire persistently during the delay period of the task.
A. Intrinsic mechanisms of graded persistent activity. A brief depolarizing stimulus to a pyramidal neuron in the entorhinal cortex elicits a short burst of
action potentials followed by an afterdepolarization (ADP) (1). A slightly longer stimulus elicits a longer burst of spikes followed by a larger
afterdepolarization (2). When the stimulus is further lengthened, the afterdepolarization is sufficient to trigger additional action potentials, leading to
2+
persistent firing
for tens
of seconds
(3).Hippocampus,
The diagram and
illustrates
a potential
mechanism
the persistent
firing.
The influx
of Ca
Source:
Prefrontal
Cortex,
the Biology
of Explicit
Memoryfor
Storage,
Principles
of Neural
Science,
Fifththrough
Editon voltage-gated
Ca2+ channels (VGCC) during an action potential opens Ca2+ -activated nonselective cation (CAN) channels. The resulting inward current through the CAN
Citation: Kandel ER, Schwartz JH, Jessell TM, Siegelbaum SA, Hudspeth AJ, Mack S. Principles of Neural Science, Fifth Editon; 2012 Available
channels produces an afterdepolarization that can lead to action potentials. The action potentials further activate VGCCs, perpetuating the cycle. The
at: http://mhmedical.com/ Accessed: May 12, 2017
recordings were obtained in the presence of carbachol, which activates muscarinic acetylcholine (ACh) receptors and a downstream signaling cascade
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that enables the opening of CAN channels when intracellular Ca is also elevated. (Reproduced, with permission, from Egorov et al. 2002.)