Pulvermuller 2002 - 14. Linguistics and the Brain

8/8/2019 Pulvermuller 2002 - 14. Linguistics and the Brain

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The Neuroscience of Language

On Brain Circuits of Wordsand Serial Order

FRIEDEMANN PULVERM ULLERCognition and Brain Sciences UnitMedical Research Council


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CHAPTER FOURTEEN

Linguistics and the Brain

Linguistics is the study of language. Language is a system of brain circuits.

To qualify the latter statement, one may cite the father of modern linguistics,

Ferdinand de Saussure, who claimed that language (i.e., the language system,

or langue) is a concrete natural object seated in the brain (de Saussure,1916). If linguistics is the study of language and language is in one sense a

system of brain circuits, one would expect linguists to be open to the study ofbrain circuits. However, the dominating view in linguistics appears to be that

language theories must be formulated in an abstract manner, not in terms

of neuron circuits. Section 14.1 asks why linguists favor abstract rather thanneuron-based formulations of language mechanisms. Section 14.2 discusses

a few thoughts about how an abstract theory of language may profit from a

brain basis.

14.1 Why Are Linguistic Theories Abstract?

As mentioned, the dominating view in linguistics is that language theories

must be formulated in an abstract way. This could be a trivial claim becauseit is clear that every scientific theory must include abstract concepts. How-

ever, this is not the point. The point is that abstractin this context excludes

explicit reference to the organic basis of the processes described in an ab-

stract fashion. Linguistic theory is abstract in the sense that it does not refer

to neurons. Why is this so?For a scientist, this may be difficult to understand. An astronomer work-

ing on star formation would probably be open to discussing molecule clouds

that can be inferred from the recordings performed (e.g., with a radio tele-

scope). The linguistic mentality, so to speak, transformed to astronomy

would result in a scholar who studies stars but refuses to speak about their

component substances and driving forces. The scholar may claim that stars

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14.1 Why Are Linguistic Theories Abstract? 271

should be discussed only in terms of abstract concepts, not in terms of gases

and their temperature.

The position that linguistic theories must be abstract appears to be in needof justification, which could be either a principled statement or an excuse.

One may argue that it is unreasonable to specify neuron circuits of lan-guage as there was no hope for a nineteenth-century astronomer to find out

about the physical processes occurring in the center of the sun that cause

emission of light. One may posit that there is simply not enough knowl-

edge about brain processes or, 100 years ago, about the interior of the

sun. However, given the immense knowledge about how the brain processes

language accumulated in the last 20 years or so, it appears more likely thatrelevant knowledge is already available for clarifying mechanisms of lan-guage in brain terms. At least, the tools appear to be available for obtaining

the crucial knowledge about the underlying physiological processes, given

there are theoretically crucial predictions.

What is necessary, then, are ideas about how to connect the level of lan-

guage description to that of the description of neurons. Piling up more neuro-

physiological and imaging data may not help much in this enterprise. Empir-

ical facts do not by themselves form a theory about the generation of sunlightor language. Theoretical work is required in the first place. The theoretical

efforts can lead to the generation of predictions that can be addressed in

crucial experiments. Lack of empirical data is never a very good excuse for

postponing the necessary theoretical labor.A reasonable excuse for not addressing language in brain terms may take

the following possibilities into consideration. Linguists may have difficulty

understanding the language of neuroscientists, and, conversely, neurosci-

entists may have difficulty understanding linguistic terminology. After all,the distance between linguistics and neuroscience is not smaller than that

between physics and chemistry. Given that such mutual comprehension dif-ficulty is relevant, the important problem may be a problem of translation

(Schnelle, 1996a, 1996c). Therefore, it may appear relevant to provide trans-

lations between the language of linguistic algorithms and that of nerve cells,

their connections, and their activity states. Again, a good deal of theoretical

work is required.

In one publication, Chomsky (2000) offers another reason for not talkingabout neuronal mechanisms of language. It may well be that the relevant

elements and principles of brain structure have yet to be discovered (p. 25).

However, brain-theoretical concepts referred to by expressions such as cell

assembly, synfire chain, and memory cellare available, and some of the po-

tentially relevant principles of brain structure and function are well under-

stood and have been available for theorizing about language for some time,


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272 Linguistics and the Brain

although language researchers have only very recently been taking advan-

tage of them. However, Chomsky is partly correct. Developing new concepts

may be necessary when theorizing about brain mechanisms of language. Themain effort undertaken in this book is to propose and sharpen concepts

for example, those labeled neuronal setand multiple reverberation.Insummary,itseemsthereisnogoodreasonwhylinguistictheoriesshould

necessarily be abstract, and why they should not be formulated in concrete

terms for example, in terms of neurons. Rather, this appears to be a crucial

linguistic task of the future.

14.2 How May Linguistic Theory Profit from a Brain Basis?

A question frequently asked by linguists is what the study of the brain couldbuy them. Clearly, if one is interested in language, one need not be interested

in the brain as well. There is absolutely no problem with this position. A

problem may arise, however, if one wishes to understand language as a

biological system, or as a brain organ, and still refuses to become concrete

about brain processes and representations (see Chomsky, 1980). In this case,

it might be advantageous to attempt to connect ones terminology to theputative mechanisms.

It is possible that translation issues can be solved and a language can be

developed that refers to linguistic structures and brain structures, linguistic

processes and brain processes, and to underlying linguistic principles, as well

as to neuroscientific principles of brain structure and function. Given sucha language is available, it would be possible to explore the space of possi-

bilities that is restricted on the one side by current neuroscientific knowl-

edge and on the other side by linguistic phenomena. Using neuroscientificknowledge and data for guiding linguistic theorizing appears to be fruitful.

Testing syntax theory in neurophysiological experiments may be fruitful as

well. Thus, neuroscientific data could then constrain linguistic theory. Thereverse may also be true. The study of language may, given such a language

connecting noun phrases to neurons (Marshall, 1980) is available, allow for

making predictions on brain circuits that have not been detected by other

means. Availability of a brainlanguage interface of this type, a neuronal

language theory, may be a necessary condition for deciding between alter-native approaches to grammar as it could be a tool for exploring neuron

circuits specific to the human brain. A language theory at the neuronal level

is required in cognitive neuroscience.

How would the situation, when performing brain imaging studies of lan-

guage, improve if a brainlanguage interface were available? It may appear

that abstract linguistic theories have some implications for neuroscientific


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14.2 How May Linguistic Theory Profit from a Brain Basis? 273

structures and processes. One may therefore claim that interesting questions

about brainlanguage relationships can already be investigated in neurosci-

entific experiments without additional theoretical work in the first place. Theargument here is that this is not true. Linguistic theories do not in fact have

strong implications regarding neuroscientific facts, and the experimenternecessarily ends up in difficulties if he or she wishes to entertain them as

research guidelines.

A rather fresh view on the relation of neuroscience and linguistics has

been put forward by Chomsky (1980) in his book, Rules and Representa-

tions. Chomsky considered how the presence of an invisible representation

of a certain kind during the processing of a sentence could be tested in anelectrophysiological experiment, taking as an example the wh- sentence

structure. Linguists assign such structures to one type of sentence, type A.

Now there is a second category of sentences, type B, for which such assign-

ment is implied by one of Chomskys theories, but not by more traditional

approaches to syntax. His proposal about the role of a neurophysiological

experiment in this theoretical issue is as follows: If a certain pattern ofelectrical activity is highly correlated with the clear cases in which a wh-

sentence is processed (type A sentences), and if this same neuronal patternalso occurs during processing of a sentence for which such a representation

has been postulated based on theoretical considerations (type B sentence),

then one would have evidence that this latter representation of the sentence

in question is psychologically and biologically real.Therefore, in principle, there appears to be no problem with the neurosci-

entific test of linguistic theories. However, Chomskys view is not realistic.

A closer look at the actual empirical data obtained so far, indicates that

clear correlation between language phenomena and patterns of electricalactivity are not easy to find. Recent studies of syntactic phenomena have

great difficulty in proving that the physiological phenomena that are re-ported to co-occur with linguistic properties of sentences are strictly related

to these linguistic properties per se. As an alternative, they may be related

to psychological phenomena in which a linguist is probably less interested,

such as working memory load and retrieval (see Kluender & Kutas, 1993).

Thus, there would not be a high correlation between a bold brain response

and a well-defined linguistic process, but there would be a brain responsecooccurring with a variety of linguistic and psychological phenomena.

But this is only the first reason why Chomskys view is not appropriate.

A further important theoretical problem that a physiological test of lin-

guistic ideas must face ignored by Chomsky is as follows: The instru-

ments for monitoring brain activity do not by themselves tell the researcherwhat to look for when investigating linguistic representations and processes.


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274 Linguistics and the Brain

There are infinite possibilities for describing and analyzing a short time series

obtained, for instance, using a multichannel electro- or magnetoencephalo-

graph. What should the language and brain scientist begin with when search-ing for the pattern that, in the clear case, correlates with the occurrence of

a wh- sentence? Answers to this question can be provided only by a theoryabout the brain mechanisms of language.

A good deal of progress being made in the language and brain sciences is

exactly of this nature: finding out what the relevant patterns of brain activity

might be. Once again, it must be stressed that brain theory reflections were

the seed of such progress.

To mention but one example, it has been speculated by a scholar whofurther developed the Hebbian brain theory (Milner, 1974) that fast oscil-

lations in the brain may be related to the activity of neuronal ensembles

(see also Freeman, 1975; von der Malsburg, 1985). Fast rhythmic brain ac-

tivity may result from reverberation of neuronal activity in loops of cortical

connections that conduct activity in the millisecond range (Chapter 8), or

they may emerge from interaction between cell assembly neurons and theirinhibitory neighbors (cf. Chapter 2). The idea that high-frequency brain ac-

tivity is related to the activation of neuronal ensembles and that it may evenbe a correlate of perceptual and higher cognitive processes inspired nu-

merous experimental investigations in the neurosciences. The results were

largely supportive (Bressler & Freeman, 1980; Singer & Gray, 1995). It was

therefore proposed that the cell assemblies, or functional webs, representingwords produce high-frequency responses when activated. On the basis of this

theoretically motivated speculation, several experiments have been con-

ducted, all of which converge on the conclusion that dynamics in high-

frequency cortical responses distinguish word forms from meaningless pseu-dowords (see Chapter 4 for details). More important, the high-frequency

responses related to word processes frequently exhibited a specific topo-graphy not revealed in other studies of high-frequency responses of cognitive

processes (Pulvermuller et al., 1997; Tallon-Baudry & Bertrand, 1999). Fur-

thermore, high-frequency brain responses recorded from motor and

visual areas distinguished between words from different categories, and may

thus reveal elementary information about more specific properties of word

processing in the brain (Pulvermuller, Keil, & Elbert, 1999; Pulvermuller,Lutzenberger et al., 1999).

In the present context, the important conclusion may be that patterns

of brain activity possibly indicating aspects of linguistic processing were

discovered only because educated guesses about the brain basis of word

processing were possible. Without the theorizing these guesses are built on,the probability of finding the patterns would have approximated zero. This


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14.2 How May Linguistic Theory Profit from a Brain Basis? 275

is the second reason why Chomskys idea about a neurobiological test of

linguistic constructs is unrealistic: He ignores the biotheoretical prerequisites

for such testing.

It can be concluded that although leading linguists may see the possible

fruitfulness of neuroscientific research into language, the nature of the major

tasks to be addressed in the theoretical neuroscience of language is largely

neglected. For serious empirical investigation of the brain mechanisms of

language, it is not enough to provide abstract descriptions of language phe-

nomena; it is also necessary to spell out possible language mechanisms in

terms of neuronal circuitry.

Building a theory of brain mechanism of language is certainly not an easytask. It is clear that such theorizing will not immediately result in the ulti-

mate answer to the relevant language-related questions. Most likely, early

proposals will be falsified by experimental brain research as, for example,

Helmholtzs idea that Gravitationsenergie causes the sun to shine had to

be replaced. However, the important point at this stage may be to make

theoretically relevant brain research on language possible. Scientific inves-

tigation of the interesting questions in linguistics requires a brain model of

the relevant linguistic processes. The purpose of this book is to give it a try.

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Pulvermuller 2002 - 14. Linguistics and the Brain