Björn Brembs

Last week, [Elizabeth
Pennisi](https://news.sciencemag.org/author/elizabeth-pennisi) asked me
to comment on the [recent paper from Schreiweis *et
al.*](https://www.pnas.org/cgi/doi/10.1073/pnas.1414542111) entitled
"Humanized FoxP2 accelerates learning by enhancing transitions from
declarative to procedural performance". Since I don't know how much, if
anything, of my answers to her questions will end up in [her
article](https://news.sciencemag.org/biology/2014/09/human-speech-gene-can-speed-learning-mice),
I thought I might expand my answer into a post about this very
interesting work.

As the title implies, Schreiweis *et al.* have tested transgenic mice in
which the mouse version of the [language-related gene
FoxP2](https://en.wikipedia.org/wiki/FOXP2) was replaced with the human
version. They found that the timing of when repeated behaviors become
stereotypic is altered, such that the behaviors become stereotypic
earlier in the humanized mice than in the unaltered animals.

Importantly, this was only observed in tasks where two learning systems
were engaged simultaneously. In the literature, there are several
accounts of how to label these learning systems. In vertebrate learning
they are often referred to as procedural vs. declarative (also in
Schreiweis *et al*.), in animal navigation many authors refer to them by
allocentric vs. egocentric, and in *Drosophila* fruit flies we have
coined the terms world- vs. self-learning. The gist behind these word
pairs is that brains as different as those from insects and mammals seem
to adhere to a common functional organization that makes a very
fundamental distinction between self and non-self on various levels. Of
relevance to the current research is that external cues are treated by
different brain regions and learning of relationships among external
cues is mediated by different molecular processes than the internal
processes controlling behavior. Hence our distinction between [world-
and self-learning](http://blogarchive.brembs.net/comment-n794.html).

In situations where both world- and self-learning can occur
simultaneously, world-learning commonly dominates in the first phases of
training, while self-learning kicks in later. There is converging
evidence from vertebrates and invertebrates suggesting that this
staggering is probably accomplished by inhibitory connections from
circuits engaged in world-learning slowing down the circuits involved in
self-learning. Thus, it is this negotiation between self- and
world-learning which provides us with time to practice our skills before
they become automatic. One may also say that this negotiation is the
reason why it takes time (and how much time it takes) to form habits.
I've written a [longer
account](http://blogarchive.brembs.net/comment-n802.html) of this
negotiation on occasion of the poster publication of some of the
Schreiweis *et al.* work in 2011.

The recently published work by Schreiweis *et al*.  now contains both
molecular genetic and physiological results in addition to the
behavioral data. It adds weight to the so-called 'motor-learning
hypothesis' that came up some time around 2006/7 or thereabout. This
hypothesis posits that FoxP2 is mainly involved in the motor, or speech
component of language, i.e., learning to control the muscles in the
lips, tongue, voice chords, etc. in order to articulate syllables and
words.The movements of these organs have to become stereotypic in order
to reliably produce understandable language and the main experimental
paradigms for this stereotypization of behavior (independent of
language) have been procedural learning and habit formation. This work
provides further evidence that indeed FoxP2 is an important component of
the learning process that leads to automatic, stereotypic behavior.

In particular, it suggests that FoxP2 is involved in the control of the
process of stereotypization, i.e., at what point the behavior shifts
from being flexible, to becoming more rigid. Until this work, the
evidence from vertebrates and invertebrates has pointed to FoxP genes to
be involved in the automatization of behavior. Now, this evidence is
extended to also -- at least in mammals -- include the negotiation
process, which I don't think anybody had on the radar thus far.

One of the most interesting mechanistic questions that derive from the
fact that these mice only showed an effect on the negotiation between
the two learning systems (and not on the individual systems when
isolated), is how this negotiation takes place. Again, converging
evidence from invertebrates and vertebrates points towards inhibitory
connections from the world-learning processes keeping a break on the
self-learning processes. Is FoxP directly affecting these inhibitory
connections, or is it just subtly increasing the relative strength of
the procedural/self mechanism, such that it cannot be detected in
individual experiments where the components have been isolated, but only
in experiments where the negotiation actually takes place? The
physiological results by Schreiweis et al. point towards the latter:
induction of [long term
depression](https://en.wikipedia.org/wiki/Long-term_depression) (LTD) in
the dorsolateral, but not the dorsomedial striatum is enhanced in the
humanized mice -- and the dorsolateral striatum is the region thought to
be involved in self-learning, while some world-learning processes have
been localized to the dorsomedial striatum.

::: {#attachment_648 .wp-caption .aligncenter style="width: 530px"}
[![The mice with the humanized version of FoxP2 form habits earlier and
this might be due to earlier formation of LTD in the dorsomedial
striatum.](https://bjoern.brembs.net/wp/wp-content/uploads/2014/09/humfoxp-1024x339.png){.size-large
.wp-image-648 fetchpriority="high" decoding="async"
aria-describedby="caption-attachment-648" width="520" height="172"
srcset="https://bjoern.brembs.net/wp/wp-content/uploads/2014/09/humfoxp-1024x339.png 1024w, https://bjoern.brembs.net/wp/wp-content/uploads/2014/09/humfoxp-300x99.png 300w, https://bjoern.brembs.net/wp/wp-content/uploads/2014/09/humfoxp.png 1805w"
sizes="(max-width: 520px) 100vw, 520px"}](https://bjoern.brembs.net/wp/wp-content/uploads/2014/09/humfoxp.png)

Mice with the humanized version of FoxP2 form habits earlier and this
might be due to earlier formation of LTD in the dorsolateral striatum.
(Fig. S7 in Schreiweis *et al*.)
:::

The generation of these humanized mice was a particularly cool aspect of
the work. Compared to other, more common transgenic manipulations (e.g.
knock-outs), this humanization of FoxP2 is a rather sophisticated and
subtle alteration with rather nuanced but nevertheless very exciting
consequences. Many of the more drastic FoxP manipulations are homozygous
lethal and since there is evidence for positive selection of the human
variant, it was very straightforward to try and see what the human
variant would do in an organism that doesn't normally express this
version. Moreover, such a subtle alteration may uncover more subtle
roles of FoxP than the cruder manipulations have been able to. In fact,
the most specific behavioral consequences of any gene manipulation have
commonly been the most subtle of genetic manipulations. Therefore, the
scientific value of this manipulation extends far beyond the fact that
it mimics the human gene.

One needs to keep in mind, though, that it was only the structure of the
protein that was humanized, the regulatory region of the gene was not
altered, i.e., the putative expression pattern of the humanized FoxP2
gene is still that of the mouse version (and I don't know how different
the human regulatory region is from the mouse one -- in fact, I'm not
sure if we have full knowledge about the regulatory region of FoxP2,
yet).

Thus, it is quite amazing that these mice showed any difference at all
to WT mice, subtle as these differences may be perceived to be.

On a wider perspective, this work adds to our growing understanding of
the relation between learning and language acquisition. Schreiweis *et
al*.'s results fall very nicely within a string of recent work
suggesting that a major component of language acquisition is based on a
form of learning called [operant
conditioning](http://blogarchive.brembs.net/comment-n734.html). The
debate about the relevance of this form of learning for language is at
the core of the idea history of neuroscience and psychology. In 1957, BF
Skinner published "[Verbal
Behavior](https://en.wikipedia.org/wiki/Verbal_Behavior)" in which he
made the sweeping claim that language was essentially acquired via
operant learning.

Two years later, Noam Chomsky took Skinner to task in what would become
one of the cornerstones in the fall of behaviorism and the rise of
cognitive neuroscience and with it, of course, Chomsky's rise to fame as
one of the US' leading intellectuals.

If one can summarize Chomsky's massive (32 pages) [book
review](https://www.chomsky.info/articles/1967----.htm) in a single
sentence, it might be: "it may look like operant learning, but you don't
have any evidence". Instead, Chomsky went on to famously propose that we
all have inborn language acquisition devices as well as 'universal
grammar'. Of course, Chomsky also did not provide any evidence,
either.In the absence of any evidence on either side, Chomsky's
outstanding rhetorical skills prevailed and changed nearly all of
psychology and neuroscience for the coming 5 decades until this day (I'm
simplifying and exaggerating somewhat, for the sake of brevity and
argument).

In the last few years, evidence has accumulated not only that the
concept of universal grammar likely is untenable, but also that indeed
operant learning (and especially the form of operant learning called
motor learning) is an important if not crucial component of language
acquisition, in particular the speech component of language. For
instance, [*FoxP* manipulations in
flies](https://bjoern.brembs.net/2014/06/the-drosophila-foxp-gene-is-necessary-for-operant-self-learning/)
specifically affect operant self-learning, but not other forms of
learning. Thus, the currently available evidence points towards an
ancestral FoxP function in self-learning, a function that is not only
conserved in humans, but one that has been further honed by evolution to
allow for the acquisition of language.This work by Schreiweis *et al*.
falls neatly within this last string of publications tilting the outcome
of this long-standing debate more and more in Skinner's favor.

As we don't know the exact mechanism by which the negotiation between
self- and world-learning processes takes place, one can only speculate
what advantage the current human version of the FoxP2 gene might have
conferred. One interesting aspect here might be that it may have been
critical for the evolution of language to speed up the stereotypization
of certain orofacial movements during the first attempts to articulate.

A further, even more tentative speculation might be that this speeding
up was adaptive, because it allowed more effective communication between
parents and their infants, at an earlier time point in the development
of the child, when it was beneficial for the vulnerable infant to convey
its status in a more nuanced way than just crying to its caregivers. In
this way, children which were able to speak earlier may have had a
survival advantage over those that spoke later.But then again, at this
time point, such speculations are merely just so stories.

On a personal note, being so used to data mostly falsifying my
hypotheses over the last 20 years, it makes me quite nervous that now in
this particular research field, everything seems to fit so well
together. If something fits so well to one's ideas, one should be
especially cautious and (beware of confirmation bias!), think hard to
make doubly sure that the next experiments are designed such that they
can easily yield results that contradict the current hypothesis, more so
than usual.

And on a side note, it is quite an irony that [three years
ago](https://bjoern.brembs.net/2014/06/why-use-fruit-flies-to-study-a-gene-involved-in-language/)
a reviewer (for the same journal that now published his work, PNAS)
heavily criticized our essentially analogous conclusions. Now, three
years later, PNAS is finally ready to publish work that supports the
motor hypothesis.

------------------------------------------------------------------------

[Schreiweis, C., Bornschein, U., Burguiere, E., Kerimoglu, C.,
Schreiter, S., Dannemann, M., Goyal, S., Rea, E., French, C., Puliyadi,
R., Groszer, M., Fisher, S., Mundry, R., Winter, C., Hevers, W., Paabo,
S., Enard, W., & Graybiel, A. (2014). Humanized Foxp2 accelerates
learning by enhancing transitions from declarative to procedural
performance [Proceedings of the National Academy of
Sciences]{style="font-style: italic;"} DOI:
[10.1073/pnas.1414542111](https://dx.doi.org/10.1073/pnas.1414542111){rev="review"}]{.Z3988
title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.jtitle=Proceedings+of+the+National+Academy+of+Sciences&rft_id=info%3Adoi%2F10.1073%2Fpnas.1414542111&rfr_id=info%3Asid%2Fresearchblogging.org&rft.atitle=Humanized+Foxp2+accelerates+learning+by+enhancing+transitions+from+declarative+to+procedural+performance&rft.issn=0027-8424&rft.date=2014&rft.volume=&rft.issue=&rft.spage=&rft.epage=&rft.artnum=http%3A%2F%2Fwww.pnas.org%2Fcgi%2Fdoi%2F10.1073%2Fpnas.1414542111&rft.au=Schreiweis%2C+C.&rft.au=Bornschein%2C+U.&rft.au=Burguiere%2C+E.&rft.au=Kerimoglu%2C+C.&rft.au=Schreiter%2C+S.&rft.au=Dannemann%2C+M.&rft.au=Goyal%2C+S.&rft.au=Rea%2C+E.&rft.au=French%2C+C.&rft.au=Puliyadi%2C+R.&rft.au=Groszer%2C+M.&rft.au=Fisher%2C+S.&rft.au=Mundry%2C+R.&rft.au=Winter%2C+C.&rft.au=Hevers%2C+W.&rft.au=Paabo%2C+S.&rft.au=Enard%2C+W.&rft.au=Graybiel%2C+A.&rfe_dat=bpr3.included=1;bpr3.tags=Medicine%2CPsychology%2CNeuroscience%2CCancer%2C+Hematology%2C+Behavioral+Neuroscience%2C+Neurolinguistics%2C+Comparative+Psychology%2C+Evolutionary+Psychology%2C+Language%2C+Learning"}


Last week, Elizabeth Pennisi asked me to comment on the recent paper from Schreiweis
<em>
 et al.
</em>
entitled “Humanized FoxP2 accelerates learning by enhancing transitions from declarative to procedural performance”. Since I don’t know how much, if anything, of my answers to her questions will end up in her article, I thought I might expand my answer into a post about this very interesting work.

Publicaciones de Rogue Scholar

Humanized FoxP2 and the timing of habits