Apical amplification—a cellular mechanism of conscious perception?

Abstract

We present a theoretical view of the cellular foundations for network-level processes involved in producing our conscious experience. Inputs to apical synapses in layer 1 of a large subset of neocortical cells are summed at an integration zone near the top of their apical trunk. These inputs come from diverse sources and provide a context within which the transmission of information abstracted from sensory input to their basal and perisomatic synapses can be amplified when relevant. We argue that apical amplification enables conscious perceptual experience and makes it more flexible, and thus more adaptive, by being sensitive to context. Apical amplification provides a possible mechanism for recurrent processing theory that avoids strong loops. It makes the broadcasting hypothesized by global neuronal workspace theories feasible while preserving the distinct contributions of the individual cells receiving the broadcast. It also provides mechanisms that contribute to the holistic aspects of integrated information theory. As apical amplification is highly dependent on cholinergic, aminergic, and other neuromodulators, it relates the specific contents of conscious experience to global mental states and to fluctuations in arousal when awake. We conclude that apical dendrites provide a cellular mechanism for the context-sensitive selective amplification that is a cardinal prerequisite of conscious perception.

Characterizing top-down microcircuitry of complex human behavior across different levels of the visual hierarchy

“…Our finding of larger task-related modulations in the outer layers in FFA (Figure 2, 3) is consistent with two theories: that of apical dendritic amplification 39 in which an already firing neuronal population receives further amplification from higher level areas to apical dendrites; and with the notion of the FFA as an intermediate stage of processing 14,40 . This effect of amplified dendritic activity has been associated with conscious perception, increasing the flexibility of neural coding by rendering it sensitive to context 41 . It has further been suggested that this mechanism of apical amplification contributes to holistic integration of information 41 , a crucial process in face perception 42 .…”

“…This effect of amplified dendritic activity has been associated with conscious perception, increasing the flexibility of neural coding by rendering it sensitive to context 41 . It has further been suggested that this mechanism of apical amplification contributes to holistic integration of information 41 , a crucial process in face perception 42 . Accordingly, the FFA may be receiving feedback, in the outer layers, from a higher level face processing region, such as the anterior inferior temporal cortex, which appears to be highly sensitive to the perceived faceness of stimuli 14 .…”

“…The results of larger top-down modulations in the outer depths of FFA and in inner depths of V1 is also consistent with the reverse hierarchy theory 44,45 . The outer layer, context specific top-down modulations in the FFA (resulting from apical amplification), would then be fed back to inner depths of V1, where pyramidal cells are located and somatic integration occurs 41 . This would serve to “select” the relevant low-level information stored in early sensory areas (in this case V1) that will subsequently be fed-forward to higher level areas to fulfill task demands.…”

Excitatory and inhibitory effects of HCN channel modulation on excitability of layer V pyramidal cells

“…Recent theoretical and empirical work suggests the mechanism of "apical amplification" [95] or "dendritic integration" [96] to be at the core of conscious processing. According to these views, only stimuli that are prioritized by contextual information reach the status of being consciously perceived.…”

Laminar Specificity of the Auditory Perceptual Awareness Negativity: A Biophysical Modeling Study

“…Such experiments have led to fundamental insight into the large-scale, network-level dynamics of conscious perception. However, despite recent experiments in animal models [4,5] and associated theoretical proposals [6][7][8] , we still lack basic understanding of the cellular-and circuit-level brain dynamics that support conscious perception, particularly across species and sensory modalities. This is likely due to inherent limitations in each neuroimaging method that hinder cellular-and circuit-level interpretation.…”