local or not

A recent press release describes a paper ( T. A. Engel, N. A. Steinmetz, M. A. Gieselmann, A. Thiele, T. Moore, K. Boahen. Selective modulation of cortical state during spatial attention. Science, 2016; 354 (6316): 1140 DOI: 10.1126/science.aag1420 ) on the neural activity during awake attention. Here is the abstract:

Neocortical activity is permeated with endogenously generated fluctuations, but how these dynamics affect goal-directed behavior remains a mystery. We found that ensemble neural activity in primate visual cortex spontaneously fluctuated between phases of vigorous (On) and faint (Off) spiking synchronously across cortical layers. These On-Off dynamics, reflecting global changes in cortical state, were also modulated at a local scale during selective attention. Moreover, the momentary phase of local ensemble activity predicted behavioral performance. Our results show that cortical state is controlled locally within a cortical map according to cognitive demands and reveal the impact of these local changes in cortical state on goal-directed behavior.

I find the techniques and the results very interesting. However, I have trouble with the idea that attention has a purely cortical mechanism. Why are the fluctuations in activity said to be endogenously generate? Why is the cortical state controlled locally within a cortical map according to cognitive demands and reveal the impact of these local changes in cortical state on goal-directed behavior? The cortex is not isolated from the rest of the brain. To say some effect is locally generated in the cortex would required showing that the activity level was not affected by the thalamus and associated parts of the brain. The back and forth between cortical columns and the thalamus is the key to cortical function and a requirement for attention, consciousness and wakefulness. This is not a new idea but has been around for a long time. Why does this study not just ignore it, but deny it?

The conclusion to a paper (Sallmann and Kastner, Cognitive and Perceptual Functions of the Visual Thalamus Neuron. 2011 Jul 28; 71(2): 209–223) outlines some signaling between various parts of the thalamus and the cortex.

The overall evidence that has emerged during recent years suggests that the visual thalamus serves a fundamental function in regulating information transmission to the cortex and between cortical areas according to behavioral context. Selective attention and visual awareness have been shown to modulate LGN (thalamus lateral geniculate nucleus) activity, thus indicating that the LGN filters visual information before it reaches the cortex. Behavioral context appears to even more strongly modulate pulvinar activity and, due to its connectivity, the pulvinar (a part of the thalamus) is well-positioned to influence feedforward and feedback information transmission between cortical areas. Because the TRN provides strong inhibitory input to both the LGN and pulvinar, the TRN (thalamic reticular nucleus) may control and coordinate the information transmitted along both retino-cortical and cortico-cortical pathways.

Parasuraman and Davis in Varieties of Attention, page 236, described the networks involved in attention as long ago as 1984.

Three interacting networks mediating different aspects of attention: (1) a posterior attention system comprising parietal cortex, superior colliculus (a midbrain area), and pulvinar(thalamus area) that is concerned was spatial attention; (2) anterior system centered on the anterior cingulate in the medial frontal lobe that mediates target detection and executive control; (3) a vigilance system consisting of the right frontal lobe and brainstem nuclei, principally the noradrenergic locus coerulus (LC).

The brain is a functioning whole not a group of completely independent parts. As the Engel group do not seem to even address the question of involvement of regions of the brain other then the cortex – how can they state that the activity level of a column is locally produced?


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