Monday, October 26, 2009

New blurbs from a new contributor

A reader reminded me recently that not enough people comment on Talking Brains. I encouraged her to contribute. Since we were just at the Neurobiology of Language conference as well as the Society for Neuroscience, I suggested she write up a few blurbs on posters/presentations that made an impression on her. Thank you, Laura Menenti (from the Donders Center), for sending this. I hope it stimulates other readers to contribute more comments on their impressions of these two meetings (or anything else, as usual).

David

(By the way, I saw these three presentations as well. All three were very provocative and interesting - nice selection, Laura.)

An idiosyncratic sample of NLC/SfN studies

Here is an idiosyncratic sample of studies I noticed at the Neurobiology of Language Conference (Oct 15th-16th) and Neuroscience 2009 (Oct 17th-21st) - idiosyncratic because the population from which to draw was huge, because the sample size needs to be small, and because the sample is biased by my own interest - naturalistic language use.

Neuroscience 2009: Characteristics of language and reading in a child with a missing arcuate fasciculus on diffusion tensor imaging. J. Yeatman, L. H. F. Barde, H.M. Feldman

Considering the importance of the arcuate fasciculus in connecting classic language areas, the question as to what language is like when you don't have one is an exciting one. The authors tested a 12-year old girl without an arcuate fasciculus (due to premature birth) patient on a standardized neuropsychological test battery, and scanned her using Diffusion-weighted Tensor Imaging (DTI). The DTI showed that indeed, the patient completely lacked the bilateral arcuate fascicule. Surprisingly, her performance on the language tests fell within the normal range. The authors conclude that normal language performance without an arcuate fasciculus is possible, and that the brain therefore shows remarkable plasticity in dealing with the lack of such an essential pathway.

There is a catch, however: in a footnote the authors mention that the subject has very 'inefficient communication' and poor academic performance. As it turns out, the girl may be able to achieve a normal score on the tests, but not in a normal way: for example, answering the question 'What is a bird?' from the Verbal Intelligence Scale takes her three minutes, according to the experimenter. It is also essentially impossible to have a conversation with her.

To me, these results show two things:

- Normal language performance is not possible without an arcuate fasciculus, assuming that being able to hold a conversation is part of normal language performance.

- The neuropsychological tests used do not properly reflect language performance if they fail to capture such gross variations in how a patient arrives at the correct answer.

It would be extremely interesting in the light of recent discussions (Hickok and Poeppel, 2004; Saur et al., 2008) to test whether this patient's impairments are restricted to specific aspects of language processing.

Neuroscience 2009: Do we click? Brain alignment as the neuronal basis of interpersonal communication. L. J. Silbert, G. Stephens, U. Hasson

In an attempt to look at normal language use, these authors target the question of how participants in a conversation achieve mutual understanding. Possibly, they do so through shared neural patterns and this study is a first step in testing that hypothesis. The authors let a speaker tell a story in the scanner and then let eleven other subjects listen to that same story. They measured correlations between the BOLD-timeseries in the speaker and the listeners. Intersubject correlations between speaker and the average listener were highest in left inferior frontal gyrus, anterior temporal lobe and precuneus/PCC. The correlations were highest when the speaker time series was shifted to precede the listeners' by 1-3 seconds, implying that the correlations are not simply due to the fact that the speaker also hears herself speak.

To corroborate the idea that these correlations underlie communication, the authors did two further tests. First, they also recorded a Russian speaker telling a story which they then presented to non-Russian listeners. They found fewer areas showing an inter-subject correlation (there were some in for instance STS). Second, they correlated the listeners' level of understanding of the story with the strength of the inter subject correlation, and found a correlation between understanding and inter-subject correlation in basal ganglia, left temporo-parietal junction and anterior cingulate cortex. The interpretation of this finding is that the more the listeners correlate with the speaker, the more they understand.

I find the purpose of studying naturalistic communication laudable, and the results are intriguing. More detailed studies of communication are necessary however: one could interpret these results as showing that language areas are involved in speaking and listening. That, in itself, is not a shocking finding. The approach, nevertheless, holds promise for more research into naturalistic communication.

NLC: The neurobiology of communication in natural settings. J. I. Skipper and J. D. Zevin

This study attempts to avoid the concern raised above, by specifying what correlations are due to what. The authors showed subjects a movie of a TV-quiz, and used Independent Components Analysis (ICA) to identify independent brain networks underlying processing of movies. After having identified the networks, they are correlated to different aspects of the movie, identified through extensive annotation of that movie. For example, they find a component that involves bilateral auditory cortices. To find out what it does, they correlate it to diverse stimulus properties as the presence/absence of speech/gesture/speech without oral movement/topic shifts/movement without speech/... (This is done through a peak and valley analysis, in which they determine the likelihood of a specific property occurring when the signal in the component is rising or falling.) For this component, the conclusion is that it is involved when speech is present. That, of course, is not a terribly shocking finding either. But, has anyone ever investigated networks sensitive to speech without visible mouth movement, speech with mouth movement but without gesture, speech with mouth movement and gesture, movement during speech that is not gesture? Only by putting all these stimulus properties in one experiment can one look both at sensitivity to these aspects of communication separately, and at the overlap between them. Importantly, the co-occurrence of all these things is what makes naturalistic communication naturalistic communication. I think this study is a great advertisement for studying language in its natural habitat.

P.S. On a more general and totally unrelated note, the Presidential Lecture at Neuroscience 2009 by Richard Morris was an absolutely impressive example of how to conduct, and to present, science.

References

Saur D, Kreher BW, Schnell S, K├╝mmerer D, Kellmeyer P, Vry M-S, Umarova R, Musso M, Glauche V, Abel S, Huber W, Rijntjes M, Hennig Jr, Weiller C (2008) Ventral and dorsal pathways for language. Proceedings of the National Academy of Sciences, 105: 18035-18040.

Hickok G, Poeppel D (2004) Dorsal and ventral streams: a framework for understanding aspects of the functional anatomy of language. Cognition 92: 67-99.

Laura Menenti

1 comment:

Greg Hickok said...

Thanks for your commentary Laura! Your analysis is spot on, as they say. I wonder if the child sans arcuate fasciculus can repeat non-words or shows a pitch-shift reflex...