(techno music)
- I'd like to tell you about some of the processes that
unfold as the baby brain grows and develops.
In particular, I'm gonna focus on the underpinnings of
language, since language learning impairment is a feature
of so many developmental disorders,
which we're gonna get into later.
So why look at baby brain function?
Because while we watch this magical unfolding of early
abilities across development we can begin to answer
some very big questions including how do early
events of development influence later cognition
and later competence.
What risk factors during early development have
consequences for adult behavior or disorder and how
might that be altered,
and how can very early abnormalities
in the functional organization of brain networks be causal
in developmental disorders such as language learning
disorder, autism, or ADHD.
And importantly, how early might biomarkers be detected,
measured, and perhaps remediated
with non-invasive technologies.
So as newborns, babies can discriminate the sounds
of every language acoustically, but not linguistically.
So starting at birth, the baby's developing brain
is constructing an acoustic map of the sounds
of his or her native language.
And this gradual process, perceptual narrowing,
is thought to be completed by the end of the first year.
Mapping of these acoustic contrasts is important
because they're salient to the surrounding language
ultimately allows the child to respond in a fast automatic
way to the incoming language stream.
And it's problematic if this doesn't go well
because it impacts mounting of fluent native language,
as well as cognition and later reading due to difficulties
in what's called phoneme-to-grapheme mapping,
that is matching speech sounds to letters,
which you need to do to read.
Efficient processing of basic auditory events in the tens
of milliseconds domain called, rapid auditory processing,
is critical to mounting language in normative development
and allows the most optimal acoustic maps to be constructed.
And this is because many speech sounds, phonemes like da or
ta, only differ by brief spectral and/or temporal changes
specifically within the tens of milliseconds.
And differences in these basic acoustic processing abilities
have been shown to be related to both concurrent
and later language learning difficulties.
Research from my lab strongly suggests that the ability
to perform these very fine acoustic discriminations
within speech or non-speech, because we mainly look
at prelinguistic non-speech, is critically important
in normative language and it may go awry in a subset
of developmental disorders.
Moreover, these skills predict language outcomes through
early pre-reading and have an impact on later learning.
So many of our studies, we examine populations
at higher risk for various disorders as a consequence
of a child being born into a family with such disorders.
And heritability studies suggest the risk
can be 30 to 60 percent higher depending on which disorder
and which study.
So how do you measure brain responses in infants?
You can use electroencephalography, EEG, which reflects
the summation of the synchronous activity of millions
of neurons that have similar spacial orientation.
You can also use brain evoked related potentials.
And this is an average across many trials
to generate an averaged waveform
that is time-locked to external stimulation.
This permits examination of the time course
in the brain areas related to sensory processing.
And you can compare and contrast group response as well as
compare individual responses to group norms.
Research suggests that brain oscillations, which are cyclic
fluctuations of the membrane potential in brain cells,
control neuronal excitability, integrate sensory inputs,
and may coordinate higher level functions,
such as language memory and learning.
However, neurodynamics was just beginning
to be studied in the human infant.
Our previous studies and pilot data strongly suggest
that oscillatory dynamics and their hierarchical
organization have a developmental timeline
and may capture disruption in normative development.
So how can you look at that?
You can look at the EEG and you can do something
called a fast Fourier analysis.
This is one way of doing it, which breaks the EEG pattern
down into its component frequencies.
Synchronized neural oscillations in these low frequencies,
delta, theta, and alpha are thought to provide
key mechanisms that orchestrate network coordination
during development and may be involved
in information transfer among brain areas.
Theta oscillations in particular are important
for perceptual and cognitive functions such as
declarative and episodic memory,
and have been proposed as a neural mechanism
subserving phonemic discrimination
which is one of the reasons we're very interested in it.
Gamma oscillations from 30 to 80 or 90 hertz
may represent synchronized activity of local neuronal
populations during sensory and cognitive processes,
but may also, particularly high gamma, play a role
in coupling of remote cortical areas.
So given that activity in this gamma frequency has been
linked in humans and animals to a wide variety of higher
cognitive processes including attention memory and language,
we first examine power density in frontal cortex
across the language bursts in two groups of children.
And I'm going to give you a few little snippets
of some studies.
We studied the power of spectra in two groups of children,
with and without a family history of language learning
impairment, at 16, 24, and 36 months of age
when this huge burst in language occurs.
We found that individual differences in frontal gamma power
during rest highly correlated with concurrent language
and cognitive skills at all ages.
Children with a family history
of language learning impairment
had lower frontal gamma at all ages.
Power was also associated with the attentional measures.
Children who were observed as having better inhibitory
control and more mature attention shifting abilities
had higher power.
We continued to follow this group
and we found that examining gamma across the language burst
strongly predicted to both cognition
and language at ages four and five years.
We saw that at 16, 24, and 36 months resting gamma
was associated with four-year language comprehension scores
and word structure and sentence structure scores.
And at 24 and 36 months gamma power was significantly
associated with five-year sentence imitation
which is really important for pre-readers.
36-month gamma power was also significantly associated
with five-year syntactical skills.
So what's the take home message here?
We believe that the capacity to generate higher power
in the gamma range at these crucial developmental periods
may index better modulation of attention,
and allow easier access to working memory,
providing an advantage for overall development
particularly in the linguistic domain.
We were then interested in examining oscillatory support
in younger infants.
So using event-related potential source localization
and a time-frequency analysis of event-related oscillation.
So from the source we examine the neural substrates
of rapid auditory processing in four month olds.
Animal models and adult experiments suggest that oscillatory
synchrony, and in particular low frequency oscillations
in the delta and theta range play key roles
in rapid auditory processing and auditory change detection.
So we hypothesized that synchronized activity
of brain oscillations in left and right auditory cortices
would support rapid frequency discrimination in infants.
Moreover, we thought that infant perception of rapid pitch
and timing changes, which is so critical,
should be mediated in part at least
by oscillatory mechanisms.
These issues had not been looked at in infants at all,
in human infants.
We used two test sets of stimuli: Speech-like tones,
(beeping tones)
and a control condition that was
out of the speech-like range.
So we found, and this is a very busy slide,
but I'll walk you through it.
You're gonna see some of these figures that show pulled
oscillatory power over time, with frequency on the X-axis,
time on the Y-axis for these complex tone pairs in the
control rate and in the rapid rate, the speech-like rate.
And these are for standards, the background sounds,
these are for deviants, the ones that change,
and this is the difference between the two.
Face synchronization is in red,
desynchronization is in blue.
And what we saw was that there was enhanced phase-locking
to variant tones in both rate conditions, larger
and faster activation in the right hemisphere at both rates.
However, left auditory activity was enhanced
only during rapid rate presentation.
We also gave these babies a go/no-go behavioral task
at their second visit.
Auditory perception was measured by the infant's ability to
learn a reward contingency for a deviant tone in a pair.
And the number of trials it took the baby
to get four out of five correct was their criterion.
And we did a median split with faster and slower learners
and what you see is that tone discrimination
is strongest for the children who learn faster.
We also saw that slower learners had smaller power
differences between their standard and deviant responses.
And this suggests that they had a lot of difficulty
discriminating one signal from another.
So the takeaway message here is that local low frequency
oscillatory synchrony underlies rapid processing
and can robustly index auditory abilities in young infants.
And recruitment of the left hemisphere during rapid
frequency change suggests a difference in the spectral
and temporal resolution of the right
and left hemispheres even at this very early age.
Moreover, we were able to predict behavior
in a go/no-go task by looking at oscillatory brainpower.
So the question is, if we can find deficits so early
in life, can we alter them using the exquisite plasticity
typical of this early developmental time period
while infants are setting up their acoustic mapping?
Can we make the baby a better processor?
And can we see intervention-specific changes
in the brain waves and oscillatory patterns
that reflect enhanced processing?
So can we look for some causal mechanisms?
And so we did a study.
We did a couple of studies.
And looking at plasticity in developing brain
and seeing if active auditory exposure would impact
pre-linguistic acoustic mapping.
And I'm gonna go through this pretty quickly,
but the paper's published if you need it.
So we looked at the neural correlates of acoustic mapping
with dense array EEG/ERP before and after a six week
interactive progressive acoustic experience.
We used an operantly-conditioned go/no-go active paradigm
with an eye-tracking control
so the baby could actually manipulate the experiment.
And we used a passive control
and a naive maturation control.
And here's the study designed two longitudinal arms,
one with active training, one with passive training,
And two, a cross-sectional sample of children
who were not trained.
So what did they get when they were trained?
Once a week for six weeks for six to eight minutes,
the babies were trained on three different types of paired
stimuli, complex tones, band-pass noise frequency sweeps
presented at varying ISIs and varying complexities
using an up-down staircase procedure.
So if the baby got it right, it got harder.
If they got it wrong, it got easier.
And so they went up and down until they reached criterion.
The passive group got the same stimuli,
and the same time exposure, but passive with no feedback
and we didn't train the naive children.
After they were trained, we collected data on ERPs, EEG
that they had been trained on, as well as different
types of generalization stimuli.
So we looked at deviance with spectral temporal parameters
that significantly differed from the training stimuli,
one with a gap, one with a differing duration,
and one with frequency.
So what did we see?
Yes, this is a monster figure.
So we're not gonna talk about the grand average waveforms.
I'm going to just pull out the information about these
time-locked age-appropriate topograms to,
first of all this P2 peak.
And this is a peak that happens that's an attentional peak.
And what we see here is around each topogram if it has a red
box, it means there was significantly faster latencies.
So the active group was significantly faster than both
the passive and the naive groups on this peak.
And then we also were interested in looking at
what's called the N2 star, and this is the change
discrimination peak that happens right before
the baby discriminates the signal.
And it's important because it's been shown to be
a robust infant predictor of later language,
So both of the auditory groups, experience groups,
were significantly faster than the naive controls,
but the actives had a larger amplitude compared to both
other groups and showed a left hemisphere lateralization.
We then looked at the signals that were a generalization
stimuli, and what you can see in these bar graphs is the
mean latency of each deviant at each
of the nine electrode sites.
For P1 that's the first sensory peak that signals
that a stimulus has been perceived.
And what you can see here for the gap, for the duration,
and frequency, is the active group was significantly
faster at all nine electrode sites.
So we demonstrated that while both active and passive
acoustic experience from four to seven months modulated
non-speech stimuli, active experience conferred
a significant advantage, that active experience increased
attention to environmental acoustic stimuli,
and that faster latencies were seen for the change
discrimination peak that has been shown to be
a robust infant predictor of later language.
Moreover, we saw generalization to both trained
and untrained stimuli over and above
that seen for maturation alone.
And do these intervention effects generalize to language?
I can just say yes, because I think we're
just about at the end.
But just let me show you this high gamma.
At nine months we continued to look at them longitudinally.
And you can see that for the actives you have this very high
gamma input here which is a prominent characteristic of
early sensory processing and may index cortical activation
given larger high, but not low gamma responses are
correlated with increases in overall firing rates
particularly during attentional modulation.
And with that I'll show you our prototype
that does the same intervention in the baby's home.
(applause)
And that's the end, thank you.
(applause)
(techno music)