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Coherence and recurrency: maintenance, control and integration in working memory.

Wolters G, Raffone A - Cogn Process (2007)

Bottom Line: A mechanism that optimizes coherent pattern segregation, also poses a limit to the number of assemblies (about four) that can concurrently reverberate.Hierarchically organized modules in PFC create the possibility for information integration.We argue that large-scale multimodal integration of information creates an 'episodic buffer', and may even suffice for implementing a central executive.

View Article: PubMed Central - PubMed

Affiliation: Department of Psychology, Institute for Psychological Research, Leiden University, Leiden, The Netherlands. wolters@fsw.leidenuniv.nl

ABSTRACT
Working memory (WM), including a 'central executive', is used to guide behavior by internal goals or intentions. We suggest that WM is best described as a set of three interdependent functions which are implemented in the prefrontal cortex (PFC). These functions are maintenance, control of attention and integration. A model for the maintenance function is presented, and we will argue that this model can be extended to incorporate the other functions as well. Maintenance is the capacity to briefly maintain information in the absence of corresponding input, and even in the face of distracting information. We will argue that maintenance is based on recurrent loops between PFC and posterior parts of the brain, and probably within PFC as well. In these loops information can be held temporarily in an active form. We show that a model based on these structural ideas is capable of maintaining a limited number of neural patterns. Not the size, but the coherence of patterns (i.e., a chunking principle based on synchronous firing of interconnected cell assemblies) determines the maintenance capacity. A mechanism that optimizes coherent pattern segregation, also poses a limit to the number of assemblies (about four) that can concurrently reverberate. Top-down attentional control (in perception, action and memory retrieval) can be modelled by the modulation and re-entry of top-down information to posterior parts of the brain. Hierarchically organized modules in PFC create the possibility for information integration. We argue that large-scale multimodal integration of information creates an 'episodic buffer', and may even suffice for implementing a central executive.

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Attentional modulation of reverberatory maintenance. Four out of the five maintained activities are of neurons (the first four neurons from below in the panels) the activities of which are selectively enhanced either by additive (voltage-independent) modulation (a), or by voltage-dependent (multiplicative) signals (b). Note that with additive modulation the membrane potentials of the four ‘focused’ neurons are higher before the stimulus onset (a), whereas the amplification mostly takes place after stimulus onset in the voltage-dependent modulation case (b)
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Fig4: Attentional modulation of reverberatory maintenance. Four out of the five maintained activities are of neurons (the first four neurons from below in the panels) the activities of which are selectively enhanced either by additive (voltage-independent) modulation (a), or by voltage-dependent (multiplicative) signals (b). Note that with additive modulation the membrane potentials of the four ‘focused’ neurons are higher before the stimulus onset (a), whereas the amplification mostly takes place after stimulus onset in the voltage-dependent modulation case (b)

Mentions: We first considered an additive (voltage-independent) input to a subset of four (the bottom four in Fig. 4a) out of eight independent IT neurons all receiving external input. This additional input was modeled in terms of additional spikes with an excitatory postsynaptic potential (EPSP) amplitude equal to the external input signals and a spiking probability equal to 0.04. As can be seen in Fig. 4a, the four items receiving top-down input exhibited a higher (subthreshold) membrane potential before the stimulus onset. This top-down bias was crucial in selecting the items to be retained in terms of reverberatory oscillations. All four biased (and one unbiased) item were maintained after stimulus offset.Fig. 4


Coherence and recurrency: maintenance, control and integration in working memory.

Wolters G, Raffone A - Cogn Process (2007)

Attentional modulation of reverberatory maintenance. Four out of the five maintained activities are of neurons (the first four neurons from below in the panels) the activities of which are selectively enhanced either by additive (voltage-independent) modulation (a), or by voltage-dependent (multiplicative) signals (b). Note that with additive modulation the membrane potentials of the four ‘focused’ neurons are higher before the stimulus onset (a), whereas the amplification mostly takes place after stimulus onset in the voltage-dependent modulation case (b)
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2254470&req=5

Fig4: Attentional modulation of reverberatory maintenance. Four out of the five maintained activities are of neurons (the first four neurons from below in the panels) the activities of which are selectively enhanced either by additive (voltage-independent) modulation (a), or by voltage-dependent (multiplicative) signals (b). Note that with additive modulation the membrane potentials of the four ‘focused’ neurons are higher before the stimulus onset (a), whereas the amplification mostly takes place after stimulus onset in the voltage-dependent modulation case (b)
Mentions: We first considered an additive (voltage-independent) input to a subset of four (the bottom four in Fig. 4a) out of eight independent IT neurons all receiving external input. This additional input was modeled in terms of additional spikes with an excitatory postsynaptic potential (EPSP) amplitude equal to the external input signals and a spiking probability equal to 0.04. As can be seen in Fig. 4a, the four items receiving top-down input exhibited a higher (subthreshold) membrane potential before the stimulus onset. This top-down bias was crucial in selecting the items to be retained in terms of reverberatory oscillations. All four biased (and one unbiased) item were maintained after stimulus offset.Fig. 4

Bottom Line: A mechanism that optimizes coherent pattern segregation, also poses a limit to the number of assemblies (about four) that can concurrently reverberate.Hierarchically organized modules in PFC create the possibility for information integration.We argue that large-scale multimodal integration of information creates an 'episodic buffer', and may even suffice for implementing a central executive.

View Article: PubMed Central - PubMed

Affiliation: Department of Psychology, Institute for Psychological Research, Leiden University, Leiden, The Netherlands. wolters@fsw.leidenuniv.nl

ABSTRACT
Working memory (WM), including a 'central executive', is used to guide behavior by internal goals or intentions. We suggest that WM is best described as a set of three interdependent functions which are implemented in the prefrontal cortex (PFC). These functions are maintenance, control of attention and integration. A model for the maintenance function is presented, and we will argue that this model can be extended to incorporate the other functions as well. Maintenance is the capacity to briefly maintain information in the absence of corresponding input, and even in the face of distracting information. We will argue that maintenance is based on recurrent loops between PFC and posterior parts of the brain, and probably within PFC as well. In these loops information can be held temporarily in an active form. We show that a model based on these structural ideas is capable of maintaining a limited number of neural patterns. Not the size, but the coherence of patterns (i.e., a chunking principle based on synchronous firing of interconnected cell assemblies) determines the maintenance capacity. A mechanism that optimizes coherent pattern segregation, also poses a limit to the number of assemblies (about four) that can concurrently reverberate. Top-down attentional control (in perception, action and memory retrieval) can be modelled by the modulation and re-entry of top-down information to posterior parts of the brain. Hierarchically organized modules in PFC create the possibility for information integration. We argue that large-scale multimodal integration of information creates an 'episodic buffer', and may even suffice for implementing a central executive.

Show MeSH
Related in: MedlinePlus