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\begin{document}

\title{Boston University NeuroPreprint Journal Club~~~~~~~~~}



\author[1]{BU NeuroPreprint Journal Club}%
\affil[1]{PREreview}%


\vspace{-1em}



  
  \date{May 20, 2024}


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\section*{}

{\label{463319}}

\textbf{A spatial code in the dorsal lateral geniculate nucleus}

Vincent Hok, Pierre-Yves Jacob, Pierrick Bordiga, Bruno Truchet,~ Bruno
Poucet, Etienne Save \textbf{}

doi: \url{https://doi.org/10.1101/473520}

Version posted on Biorxiv: 11/19/18

\section*{}

{\label{463319}}

In the current work, Hok et al. report the existence of spatial
receptive fields in the dLGN of rats that are similar in nature to HPC
place fields. The authors demonstrate that dLGN place fields, which make
up approximately 30\% of extracellularly recorded dLGN neurons, are less
stable and more variable (on a pass by pass basis) than their HPC
counterparts. Further, the authors show theta oscillations in the dLGN
local field potential and the presence of individual dLGN neurons that
have theta rhythmic spiking. The authors report that, unlike CA3
neurons, most dLGN neurons do not exhibit theta phase precession
suggesting that the dLGN spatial code does not carry sequential
information about the animal's current, past, or future trajectories.
Finally, Hok and colleagues show that a sub-population of dLGN neurons
can be modulated by visual stimulation but that this population does not
overlap with neurons that exhibit place fields. Interestingly, dLGN
place fields are insensitive to the presence or absence of visual
information (as determined by similarity in responses in recordings from
light vs. dark conditions) but remap when the color of the environment
is altered (from all white to all black).

~

By and large the results are robust and the reported findings will be of
interest to researchers considering interactions between different forms
of neural spatial representations and visual information. Further, the
observation of spatial receptive fields in the dLGN raises important
questions about fundamentals of visual processing. We enjoyed the
manuscript and have the following suggestions for the authors.

\par\null

\textbf{Major suggestions:}

\par\null

* There is little discussion about dLGN visual sensitivity in the rat
despite there being extensive literature on the subject. There is known
retinotopy in dLGN (see for example, Montero et al. 1968). How, if at
all, does this relate to the spatial response properties of dLGN
neurons? For example, is there any correspondence between neurons that
would be sensitive to the lower half of the visual field and remapping
in the light vs. dark arena conditions? A similar question could be
raised regarding the object sensitive sub-population. The authors should
attempt to address the relationship between their observations and
visual sensitivity of dLGN in more detail.

* The object sensitive sub-population is intriguing, but the details
concerning this finding are ambiguous. It is mentioned briefly in the
main manuscript but the percentage of neurons exhibiting this tendency
is unclear, even when examining the extended data concerning this
observation. As a result, the reader is left a bit distracted by this
information, especially when considering that object sensitive neurons
are not place cells. The authors should consider presenting this
component of the manuscript in greater detail.

\par\null

* The visual stimulation experiment is posed as a control for
determining that dLGN place cells were indeed recorded in a visually
sensitive area (dLGN), but this experiment was not conducted for CA3
neurons. How can we know for certain that the visual stimulation
protocol wouldn't have elicited modulation in CA3 neurons as well, thus
rendering this component of the study inconclusive?

* Tissue can often become displaced for extended periods of time when
moving tetrodes along the D/V axis. How confident are the authors in the
correspondence between their tetrode turning records and final tetrode
placement? The waveform related analyses are pretty convincing and seems
to cluster nicely into two groups, but waveform shape is not a
definitive metric for determining the location of a recorded neuron. Is
it possible to record from dLGN without moving electrodes through the
hippocampus first? It would be helpful if the authors could provide more
histology so readers can examine for themselves how displaced CA3 tissue
was.

\par\null

* It seems that LFPs were primarily referenced to another tetrode.
Instead, LFPs should be referenced against an electrode outside of
either the hippocampus or dLGN such as a skull screw above the
cerebellum. Because of the current referencing scheme and many other
factors, theta oscillations recorded in the dLGN could be explained by
volume conduction yet this is not considered. These issues may be of
great importance to the theta phase precession analysis. Did the authors
attempt to look at phase precession for dLGN place cells against both
HPC LFPs as well as dLGN LFPs? If not, this would be an important
analysis to consider.

* No power spectral density plots are shown for theta oscillations in
CA3 and dLGN. It would be interesting to see if the dLGN theta peak in
the power spectrum is broader compared to CA3, which might explain the
higher theta frequency and would also affect phase-related analyses.
Additionally, a consideration of speed related modulation of theta
dynamics should likely be included.

\section*{}

{\label{463319}}

\textbf{Minor Concerns:}

* Table 1 should include a \#/\% of cells which were ``object specific''

\par\null

* Re Overdispersion analysis (line 460): A linearly scaled Poisson
distribution will itself be poisson distributed, not normal, with the
approximation being more valid at higher firing rates. The Z value
described here will therefore be biased to higher values for lower
firing rate neurons. Because of this, it is unclear if the results in
lines 90-92 are artificially strong or weak. If thalamic neurons have a
higher firing rate than CA3 neurons, they may have an even higher
difference in dispersion than reported. A consideration of percentiles
rather than standard deviations would likely be revealing.

* Quantification of the object rotation sub-experiment (lines 144-147)
should be included in the main manuscript text.

\par\null

* More details on the properties of theta modulation in dLGN should be
presented. What percentage of dLGN neurons had peaks in the theta
frequency range in the FFT of their spike train autocorrelations (i.e.
how many were significantly theta rhythmic)? What percentage of dLGN
neurons were theta phase locked and was there a bias to a particular
theta phase? Was theta oscillatory activity for single dLGN neurons
modulated by running speed?

\par\null

* Was a velocity filter used when creating spatial firing rate maps? In
a related point, did the authors examine potential differences in mobile
vs. immobile activation for dLGN vs. HPC?

\par\null

* Perhaps we missed it, but what size was the smoothing kernel for 2D
ratemaps (in cms)?

\par\null

* Did the authors examine the spatial distribution of dLGN place fields
and, if so, were they uniformly distributed? It would be interesting to
know if the fields clustered near objects for example.

\par\null

* The explanation of the ``field index'' metric is difficult to
understand in the methods and should be clarified if possible.

\par\null

Figure 2:~ The color-coded pass index trajectory plots are not very
informative because the dots are all layered on top of each other.
Authors could do one or multiple of the following to enhance
interpretation: make the dots smaller, make the dots transparent, make
the color map sequential rather than qualitative. It would also be
helpful to provide an ``n'' of the number of place cells in each region
in Fig 2g.

\par\null

Figure 3:~ The close up of a single pass in the upper right corner of
sub-plots 3b and 3c are confusing. The legend could be revised to
clarify what we are looking at. In general, we are a bit unclear as to
why the close up of a single pass is necessary. Are we supposed to see
rhythmic activity in the spikes? The close up of a single pass is not
useful for this because the rat may not be moving at a constant
velocity. It may be the case that the spike train above is sufficient.

- BU NeuroPreprint JC

\par\null

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