Layer and regional effects of environmental enrichment on the pyramidal neuron morphology of the rat

The environmental enrichment (EE) paradigm is widely used to study experience-dependent brain plasticity. Several studies have investigated functional and anatomical EE effects. However, as EE effects are different according to cerebral region, cortical layer, dendritic field and morphological index considered, a univocal characterization of neuronal morphological changes following rearing in enriched environments is lacking.Aim of the present study was to characterize in the rat the effects of EE on the neuronal morphology of frontal and parietal cortical regions, the main target areas of the stimulation provided by the paradigm. Male Wistar rats were housed in an enriched environment for 3.5 months from the 21st postnatal day. For the morphological analysis, biotinylated dextran amine (BDA)-labeled pyramidal neurons were selected from frontal (M1–M2) and parietal (S1–S2) cortical layers III and V. Apical and basal dendritic branching and spines were analyzed using the Sholl method.Results showed that EE increased branching and spines in both layers of frontal cortex, but had a greater effect on apical arborization. In parietal cortex, EE significantly affected branching and spines in layer III but not layer V neurons, in which only a tendency to be influenced by the rearing conditions was observed in basal arborization.It is hypothesized that these multifaceted morphological EE effects are connected to the heavy involvement of a sensory-motor circuit engaged in the guidance of voluntary action and in motor learning activated by EE stimulation.     

From synaptic transmission to cognition: an intermediary role for dendritic spines

Dendritic spines are cytoplasmic protrusions that develop directly or indirectly from the filopodia of neurons. Dendritic spines mediate excitatory neurotransmission and they can isolate the electrical activity generated by synaptic impulses, enabling them to translate excitatory afferent information via several types of plastic changes, including neoformation, disappearance, redistribution and changes in geometric shape. The fine line between normal and abnormal excitatory neurotransmission is mediated by the concerted action of glutamate-mediated stimulation and calcium ion entry into spines. Moreover, within the range of normal excitatory activity, dendritic spines undergo specific plastic changes to regulate different forms of afferent information that are often related to distinct modes of cognition-related electrophysiological stimulation, such as long-term potentiation or long-term depression.     

The brain is both neurocomputer and quantum computer

In their article, Is the Brain a Quantum Computer,? Litt, Eliasmith, Kroon, Weinstein, and Thagard (2006) criticize the Penrose–Hameroff “Orch OR” quantum computational model of consciousness, arguing instead for neurocomputation as an explanation for mental phenomena. Here I clarify and defend Orch OR, show how Orch OR and neurocomputation are compatible, and question whether neurocomputation alone can physiologically account for coherent gamma synchrony EEG, a candidate for the neural correlate of consciousness. Orch OR is based on quantum computation in microtubules within dendrites in cortex and other regions linked by dendritic–dendritic gap junctions (“dendritic webs”) acting as laterally connected input layers of the brain's neurocomputational architecture. Within dendritic webs, consciousness is proposed to occur as gamma EEG‐synchronized sequences of discrete quantum computational events acting in integration phases of neurocomputational “integrate‐and‐fire” cycles. Orch OR is a viable approach toward understanding how the brain produces consciousness.