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Feature: Chou P. Hung

Published June 1, 2014

ChouDrs Chou P. Hung, Chia-pei Lin, and Yueh-peng Chen recently published a paper titled "Tuning and spontaneous spike time synchrony share a common structure in macaque inferior temporal cortex."

NeuroNexus caught up Dr. Chou to discuss his work, techniques, and potential applications for humans.

 


Q: Your study was performed on primates. Do you think the findings are directly applicable for humans? If not, what are the differences that you might expect?

The short answer is, "yes." Previously, it was thought that the more differently cells behave, the more information they carry. Our study says that instead, it is the cells that behave more similarly, the ‘choristers,’ that carry the useful information. The other cells, the ‘soloists,’ may fine-tune the patterns. The dense spacing of these arrays, about 32 channels per cortical column, was critical to measuring this correlated activity. For ethical reasons, we can't make the same recordings in humans, but our preliminary data indicate that this activity in primates is linked to coarser signals in human functional imaging and to human psychophysics. Understanding these issues is important to unraveling how we learn and what goes wrong in mental diseases, where studies have found altered correlated activity in functional magnetic resonance imaging (fMRI) but the link to single neurons has not been made.

Q: Your study found that “tuning and spike synchrony were linked by a common spatial structure that is highly efficient for Object representation.” What is the next step in this research?

In autism and other brain diseases, brain imaging signals have different patterns, but it has been difficult to link these coarser patterns to mechanisms in single cells. It would be helpful if we had a better understanding of how different signal types are linked in the same animal. Also, how the brain recognizes visual information is an extremely challenging problem. It is much harder than reasoning. Understanding how the brain processes information is key to understanding how the brain creates intelligence. To do this, we would like to better understand what are the roles of the choristers versus the soloists. If our hypothesis is correct, the choristers and soloists should have different roles in learning and behavior. We would like to find the underlying principles and to apply them, at a suitable level of abstraction, in computational models. These are among the goals outlined in the Brain Initiative, and the dense spatiotemporal sampling enabled by these arrays is critical to meeting these goals.

Q: You were recording with 64-channel probes that had a planar design. In your perfect world, how many sites would you like to be able to record from simultaneously to get the optimal contrast/area coverage for similar visual studies?

Lin 2014 Tuning and spontaneous spike time synchrony share a common structure in macaque inferior temporal cortex

ARRAY RECORDING OF IT OBJECT RESPONSES

Having 64 channels in two cortical columns is already very good, because it lets us hear correlated single-unit activity that would be missed at coarser resolutions. Theoretically, the effects of correlated activity are amplified in densely connected, homogeneous populations. But, because neurons are very heterogeneous, even within a cortical column, dense sampling is necessary to hear the correlated activity. Our preliminary data indicate that at least ~8 channels per cortical column are needed to measure an effect of noise correlation on object coding, and the effect size increases at higher density. This threshold might vary across cortical areas - in our studies, about half the V1 neuronal pairs in an array were correlated, versus only about 6% in inferior temporal cortex, during spontaneous activity. This may have to do with the increasing complexity of the representation along the ventral visual pathway. In a perfect world, it might be good to increase the range of depth, because 1.4 mm isn't quite enough to sample all cortical layers simultaneously. But, there is a tradeoff in the signal quality as you increase the number of contacts.

Q: Would a 3-dimensional probe (with the ability to span both cortical columns and cortical layers) benefit your research? If so, in what way?

Definitely, a 3D array would help. Having a 3D array would give us a clearer picture of phenomena such as surround inhibition, and it would aid in efforts to link spiking activity to functional imaging in the same animal. Going to 3D may also improve chronic stability, so that we can track changes in the activity patterns during learning. Also, 3D would help with the issue of having sufficient spatial density, to 'hear' the neurons that are strongly interconnected and that 'care' about the animal's behavioral task.