Cognitive Neuroscience Arena

Introducing Cognitive Neuroscience

"Jamie Ward has done a great service to the neuroscience community: he has written an easy to read, enjoyable introduction to cognitive neuroscience that will attract many students to the discipline. I will certainly use this book for my courses." - Professor Alfonso Caramazza, Harvard University

Between 1928 and 1947, Wilder Penfield and colleagues carried out a series of remarkable experiments on over 400 living human brains (e.g. Penfield & Rasmussen, 1950). The patients in question were undergoing brain surgery for epilepsy.

To identify and spare regions of the brain involved in movement and sensation, Penfield electrically stimulated regions of the cortex while the patient was still conscious. The procedure was not painful (the surface of the brain does not contain pain receptors) but the patients did report some fascinating experiences.

When stimulating the occipital lobe one patient reported "a star came down towards my nose". Upon stimulating a region near the central sulcus, another patient commented "those fingers and my thumb gave a jump". After temporal lobe stimulation, another patient claimed "I heard the music again; it is like the radio". She was later able to recall the tune she heard and was absolutely convinced that there must have been a radio in the operating theatre.

Of course, the patients had no idea when the electrical stimulation was being applied – they couldn't physically feel it or see it. As far as they were concerned, an electrical stimulation applied to the brain felt pretty much like a mental/cognitive event.

This book tells the emerging story of how mental processes such as thoughts, memories, and perceptions are organized and implemented by the brain. It is also concerned with how it is possible to study the mind and brain, and how we know what we know.

The term cognition collectively refers to a variety of higher mental processes such as thinking, perceiving, imagining, speaking, acting and planning.

Cognitive neuroscience is a bridging discipline between cognitive science and cognitive psychology, on the one hand, and biology and neuroscience, on the other. It has emerged as a distinct enterprise only recently and has been driven by methodological advances that enable the study of the human brain safely in the laboratory.

It is perhaps not too surprising that earlier methods, such as direct electrical stimulation of the brain, failed to enter into the mainstream of research.

This chapter begins by placing a number of philosophical and scientific approaches to the mind and brain in an historical perspective.

The coverage is selective rather than exhaustive, and students with a particular interest in these issues might want to read more deeply elsewhere (e.g. Gross, 1998). The chapter then provides a basic overview of the current methods used in cognitive neuroscience.

A more detailed analysis and comparison of the different methods is provided in Chapters 3 to 5. Finally, the chapter attempts to address some of the criticisms of the cognitive neuroscience approach that have recently been articulated.

A timeline for the development of methods and findings relevant to cognitive neuroscience, from phrenology to present day.

Cognitive Neuroscience in Historical Perspective

Philosophical Approaches to Mind and Brain

Philosophers as well as scientists have long been interested in how the brain could create our mental world. How is it that a physical substance can give rise to our feelings, thoughts and emotions? This has been termed the mind–body problem, although it should more properly be called the mind–brain problem because it is now agreed that the brain is the key part of the body for cognition.

One position is that the mind and brain are made up of different kinds of substance, even though they may interact. This is known as dualism, and the most famous proponent of this idea was René Descartes (1596–1650). Descartes believed that the mind was non-physical and immortal whereas the body was physical and mortal. He suggested that they interact in the pineal gland, which lies at the centre of the brain and is now considered part of the endocrine system.

According to Descartes, stimulation of the sense organs would cause vibrations in the body/brain that would be picked up in the pineal gland, and this would create a non-physical sense of awareness.

There is little hope for cognitive neuroscience if dualism is true because the methods of physical and biological sciences cannot tap into the non-physical domain (if such a thing were to exist).

Even in Descartes' time, there were critics of his position. One can identify a number of broad approaches to the mind–body problem that still have a contemporary resonance. Spinoza (1632–1677) argued that mind and brain were two different levels of explanation for the same thing, but not two different kinds of thing.

This has been termed dual-aspect theory and it remains popular with some current researchers in the field (e.g. Velmans, 2000). An analogy can be drawn to wave-particle duality in physics in which the same entity (e.g. an electron) can be described both as a wave and as a particle.

An alternative approach to the mind–body problem that is endorsed by many contemporary thinkers is reductionism (e.g. Churchland, 1995; Crick, 1994). This position states that although cognitive, mind-based concepts (e.g. emotions, memories, attention) are currently useful for scientific exploration, they will eventually be replaced by purely biological constructs (e.g. patterns of neuronal firings, neurotransmitter release). As such, psychology will eventually reduce to biology as we learn more and more about the brain.

Advocates of this approach note that there are many historical precedents in which scientific constructs are abandoned when a better explanation is found.

In the seventeenth century, scientists believed that flammable materials contained a substance, called phlogiston, which was released when burned. This is similar to classical notions that fire was a basic element along with water, air and earth.

Eventually, this construct was replaced by an understanding of how chemicals combine with oxygen. The process of burning became just one example (along with rusting) of this particular chemical reaction.

Reductionists believe that mind-based concepts, and conscious experiences in particular, will have the same status as phlogiston in a future theory of the brain.

Those who favour dual-aspect theory over reductionism point out that an emotion will still feel like an emotion even if we were to fully understand its neural basis and, as such, the usefulness of cognitive, mind-based concepts will never be fully replaced.

Scientific Approaches to Mind and Brain

Our understanding of the brain emerged historically late, largely in the nineteenth century, although some important insights were gained during classical times.

Aristotle (384–322 BC) noted that the ratio of brain size to body size was greatest in more intellectually advanced species, such as humans.

Unfortunately, he made the error of claiming that cognition was a product of the heart rather than the brain. He believed that the brain acted as a coolant system: the higher the intellect, the larger the cooling system needed.

In the Roman age, Galen (circa AD 129–199) observed brain injury in gladiators and noted that nerves project to and from the brain. Nonetheless, he believed that mental experiences themselves resided in the ventricles of the brain.

This idea went essentially unchallenged for well over 1500 years. For example, when Vesalius (1514–1564), the father of modern anatomy, published his plates of dissected brains, the ventricles were drawn in exacting detail whereas the cortex was drawn crudely and schematically. Others followed in this tradition, often drawing the surface of the brain like the intestines. This situation probably reflected a lack of interest in the cortex rather than a lack of penmanship.

It is not until one looks at the drawings of Gall and Spurzheim (1810) that the features of the brain become recognizable to modern eyes.

Gall (1758–1828) and Spurzheim (1776–1832) received a bad press, historically speaking, because of their invention and advocacy of phrenology.

Phrenology had two key assumptions. First, that different regions of the brain perform different functions and are associated with different behaviours. Second, that the size of these regions produces distortions of the skull and correlates with individual differences in cognition and personality.

Taking these two ideas in turn, the notion of functional specialization within the brain has effectively endured into modern cognitive neuroscience, having seen off a number of challenges over the years (Flourens, 1824; Lashley, 1929). The observations of Penfield and co-workers on the electrically stimulated brain provide some striking examples of this principle.

However, the functional specializations of phrenology were not empirically derived and were not constrained by theories of cognition. For example, Fowler's famous phrenologist's head had regions dedicated to "parental love", "destructiveness" and "firmness". Moreover, skull shape has nothing to do with cognitive function.

Different drawings of the brain from Vesalius (1543) (top), de Viessens (1685) (bottom left), and Gall and Spurzheim (1810) (bottom right). Note how the earlier two drawings emphasized the ventricles and/or misrepresented the cortical surface.

Aside from inventing phrenology, Gall and Spurzheim made a number of important anatomical observations, such as delineating between the functions of white and grey matter, and the realization that the brain is folded to conserve space (see Gross, 1998).

Their empirical observations and theoretical insights paved the way for future developments in the nineteenth century, the most notable of which are Broca's reports of two brain-damaged patients (Broca, 1861).

Broca documented two cases in which acquired brain damage had impaired the ability to speak but left other aspects of cognition relatively intact. He concluded that language could be localized to a particular region of the brain. Subsequent studies argued that language itself was not a single entity but could be further subdivided into speech recognition, speech production and conceptual knowledge (Lichtheim, 1885; Wernicke, 1874).

This was motivated by the observation that brain damage can lead either to poor speech comprehension and good production, or good speech comprehension and poor production (see Chapter 10 for full details). This suggests that there are at least two speech faculties in the brain and that each can be independently impaired by brain damage.

This body of work was a huge step forward in terms of thinking about mind and brain. First, empirical observations were being used to determine what the building blocks of cognition are (is language a single faculty?) rather than listing them from first principles. Second and related, they were developing models of cognition that did not make direct reference to the brain. That is, one could infer that speech recognition and production were separable without necessarily knowing where in the brain they were located, or how the underlying neurons brought these processes about.

The approach of using patients with acquired brain damage to inform theories of normal cognition is called cognitive neuropsychology and remains highly influential today (Chapter 5 discusses the logic of this method in detail).

Cognitive neuropsychology is now effectively subsumed within the term "cognitive neuroscience", where the latter phrase is seen as being less restrictive in terms of methodology.

Whereas discoveries in the neurosciences continued apace throughout the nineteenth and twentieth centuries, the formation of psychology as a discipline at the end of the nineteenth century took the study of the mind away from its biological underpinnings. This did not reflect a belief in dualism. It was due, in part, to some pragmatic constraints. Early pioneers of psychology, such as William James and Sigmund Freud, were interested in topics like consciousness, attention, and personality. Neuroscience has had virtually nothing to say about these issues until quite recently.

Another reason for the schism between psychology and biology lies in the notion that one can develop coherent and testable theories of cognition that do not make claims about the brain. The modern foundations of cognitive psychology lie in the computer metaphor of the brain and the information processing approach, popular from the 1950s onwards.

For example, Broadbent (1958) argued that much of cognition consists of a sequence of processing stages. In his simple model, perceptual processes occur, followed by attentional processes that transfer information to short-term memory and thence to long-term memory (see also Atkinson & Shiffrin, 1968). These were often drawn as a series of box-and-arrow diagrams.

The implication was that one could understand the cognitive system in the same way as one could understand the series of steps performed by a computer program, and without reference to the brain. The idea of the mind as a computer program has advanced over the years along with advances in computational science.

For example, many cognitive models contain some element of interactivity and parallel processing. Interactivity refers to the fact that stages in processing may not be strictly separate and that later stages can begin before earlier stages are complete. Moreover, later stages can influence the outcome of early ones (top-down processing).

Examples of box-and-arrow and connectionist models of cognition. Both represent ways of describing cognitive processes that need not make direct reference to the brain.

Parallel processing refers to the fact that lots of different information can be processed simultaneously (serial computers process each piece of information one at a time). Although these computationally explicit models are more sophisticated than earlier box-and-arrow diagrams they, like their predecessors, do not always make contact with the neuroscience literature (Ellis & Humphreys, 1999).

The Birth of Cognitive Neuroscience

It was largely advances in imaging technology that provided the driving force for modern-day cognitive neuroscience.

Raichle (1998) describes how brain imaging was in a "state of indifference and obscurity in the neuroscience community in the 1970s" and might never have reached prominence if it were not for the involvement of cognitive psychologists in the 1980s.

Cognitive psychologists had already established experimental designs and information-processing models that could potentially fit well with these emerging methods. It is important to note that the technological advances in imaging not only led to the development of functional imaging, but also enabled brain lesions to be described precisely in ways that were never possible before (except at post mortem).

Present-day cognitive neuroscience is composed of a broad diversity of methods. These will be discussed in detail in subsequent chapters.

At this juncture, it is useful to compare and contrast some of the most prominent methods. The distinction between recording methods and stimulation methods is crucial in cognitive neuroscience. Electrical stimulation of the brain in humans is now rarely carried out.

The modern-day equivalent of these studies uses magnetic, not electric, fields and is called transcranial magnetic stimulation (TMS). These can be applied across the skull rather than directly to the brain. This method will be considered in Chapter 5, alongside the effect of organic brain lesions.

Electrophysiological methods (EEG/ERP and single-cell recordings) and magnetophysiological methods (MEG) record the electrical/ magnetic properties of neurons themselves. These methods are considered in Chapter 3.

In contrast, functional imaging methods (PET and fMRI) record physiological changes associated with blood supply to the brain which evolve more slowly over time. These are called haemodynamic methods and are considered in Chapter 4. The methods of cognitive neuroscience can be placed on a number of dimensions:

• The temporal resolution refers to the accuracy with which one can measure when an event is occurring. The effects of brain damage are permanent and so this has no temporal resolution as such. Methods such as EEG, MEG, TMS and single-cell recording have millisecond resolution. PET and fMRI have temporal resolutions of minutes and seconds, respectively, that reflect the slower haemodynamic response.
• The spatial resolution refers to the accuracy with which one can measure where an event is occurring. Lesion and functional imaging methods have comparable resolution at the millimetre level, whereas single-cell recordings have spatial resolution at the level of the neuron.
• The invasiveness of a method refers to whether or not the equipment is located internally or externally. PET is invasive because it requires an injection of a radio-labelled isotope. Single-cell recordings are performed on the brain itself and are normally only carried out in non-human animals.

The different methods used in cognitive neuroscience.

Method	Method type	Invasiveness	Brain property used
EEG/ERP	Recording	Non-invasive	Electrical
Single-cell (and multi-unit) recordings	Recording	Invasive	Electrical
TMS	Stimulation	Non-invasive	Electromagnetic
MEG	Recording	Non-invasive	Magnetic
PET	Recording	Invasive	Haemodynamic
fMRI	Recording	Non-invasive	Haemodynamic

The methods of cognitive neuroscience can be categorized according to their spatial and temporal resolution. Adapted from Churchland and Sejnowski, 1988.

Does Cognitive Psychology Need the Brain?

As already noted, cognitive psychology developed substantially from the 1950s, using information-processing models that do not make direct reference to the brain. If this way of doing things remains successful, then why change?

Of course, there is no reason why it should change. The claim is not that cognitive neuroscience is replacing cognitive psychology (although some might endorse this view) but merely that cognitive psychological theories can inform theories and experiments in the neurosciences and vice versa.

However, others have argued that this is not possible by virtue of the fact that informationprocessing models do not make claims about the brain (Coltheart, 2004b; Harley, 2004).

One could take many different measures in a forced-choice response task: behavioural (reaction time [RT], errors) or biological (electromyographic [EMG], lateralized readiness potential [LRP], lateralized BOLD response [LBR]). All measures could potentially be used to inform cognitive theory. Adapted from the Quarterly Journal of Experimental Psychology, 58A (2), 193-233, What can functional neuroimaging tell the experimental psychologist?, 2005, by kind permission of the Experimental Psychology Society.

Coltheart (2004b) poses the question: "Has cognitive neuroscience, or if not might it ever (in principle, or even in practice) successfully use data from cognitive neuroimaging to make theoretical decisions entirely at the cognitive level (e.g. to adjudicate between competing information-processing models of some cognitive system)?" (p. 21).

Henson (2005) argues that it can in principle and that it does in practice. He argues that data from functional imaging (blood flow, blood oxygen) comprise just another dependent variable that one can measure. For example, there are a number of things that one could measure in a standard forced-choice reaction-time task: reaction time, error rates, sweating (skin conductance response), muscle contraction (electromyograph), scalp electrical recordings (EEG) or haemodynamic changes in the brain (PET, fMRI). Each measure will relate to the task in some way and can be used to inform theories about the task.

To illustrate this point, consider one example. One could ask a simple question such as: "does visual recognition of words and letters involve computing a representation that is independent of case?" For example, does the reading system treat "E" and "e" as equivalent at an early stage in processing or are "E" and "e" treated as different letters until some later stage (e.g. saying them aloud)?

A way of investigating this using a reaction-time measure is to present the same word twice in the same or different case (e.g. radio-RADIO, RADIO-RADIO) and compare this with situations in which the word differs (e.g. mouse-RADIO, MOUSE-RADIO).

One general finding in reaction-time studies is that it is faster to process a stimulus if the same stimulus has recently been presented. For example, if asked to make a speeded decision about RADIO (e.g. is it animate or inanimate) then performance will be faster if it has been previously encountered. Dehaene et al. (2001) investigated this mechanism by comparing reaction-time measures with functional imaging (fMRI) measures.

In his task, the first word in each pair was presented very briefly and was followed by visual noise. This prevents the participants from consciously perceiving it and, hence, one can be sure that they are not saying the word. The second word is consciously seen and requires a response.

Dehaene et al. found that reaction times are faster to the second word when it follows the same word, irrespective of case. Importantly, there is a region in the left fusiform cortex that shows the same effect (although in terms of "activation" rather than response time). In this concrete example, it is meaningless to argue that one type of measure is "better" for informing cognitive theory (to return to Coltheart's question) given that both are measuring different aspects of the same thing.

One could explore the nature of this effect further by, for instance, presenting the same word in different languages (in bilingual speakers), presenting the words in different locations on the screen and so on. This would provide further insights into the nature of this mechanism (e.g. what aspects of vision does it entail, does it depend on word meaning). However, both reaction-time measures and brain-based measures could be potentially informative. It is not the case that functional imaging is merely telling us where cognition is happening and not how it is happening.

Both reaction times and fMRI activation in the left fusiform region demonstrate more efficient processing of words if they are preceded by subliminal presentation of the same word, irrespective of case. Adapted from Dehaene et al., 2001.

Another distinction that has been used to contrast cognitive psychology and cognitive neuroscience is that between software and hardware, respectively (Coltheart, 2004b; Harley, 2004). This derives from the familiar computer analogy in which one can, supposedly, learn about information processing (software) without knowing about the brain (hardware).

As has been shown, to some extent this is true. But the computer analogy is a little misleading. Computer software is written by computer programmers (who, incidentally, have human brains). However, information processing is not written by some third person and then inscribed into the brain. Rather, the brain provides causal constraints on the nature of information processing. This is not analogous to the computer domain in which the link between software and hardware is arbitrarily determined by a computer programmer.

To give a simple example, one model of word recognition suggests that words are recognized by searching words in a mental dictionary one by one until a match is found (Forster, 1976). The weight of evidence from cognitive psychology argues against this serial search, and in favour of words being searched in parallel (i.e. all candidate words are considered at the same time). But why should this be so? Computer programs can be made to recognize words adequately with both serial search and parallel search.

The reason why human information processing uses a parallel search and not a serial search probably lies in the relatively slow neural response time (acting against serial search). This constraint does not apply to the fast processing of computers.

Thus, cognitive psychology may be sufficient to tell us the structure of information processing but it may not answer deeper questions about why information processing should be configured in that particular way.

The media loves to simplify the findings of cognitive neuroscience. Many newspaper stories appear to regard it as counterintuitive that sex, pain and mood would be products of the brain. Sunday Times 21 November 1999; Metro 5 January 2001; The Observer 12 March 2000; The Independent 27 May 1999.

Does Neuroscience Need Cognitive Psychology?

It would be no exaggeration to say that the advent of techniques such as functional imaging have revolutionized the brain sciences.

For example, consider some of the newspaper headlines above that have appeared in recent years. Of course, it has been well known since the nineteenth century that pain, mood, intelligence and sexual desire would be largely a product of processes in the brain.

The reason why headlines such as these are extraordinary is because now the technology exists to be able to study these processes in vivo. Of course, when one looks inside the brain one does not "see" memories, thoughts, perceptions and so on (i.e. the stuff of cognitive psychology). Instead, what one sees is grey matter, white matter, blood vessels and so on (i.e. the stuff of neuroscience).

It is the latter, not the former, that one observes when conducting a functional imaging experiment. Developing a framework for linking the two will necessarily entail dealing with the mind–body problem either tacitly or explicitly. This is a daunting challenge.

Is functional imaging going to lead to a more sophisticated understanding of the mind and brain than was achieved by the phrenologists? Some of the newspaper reports in the figure suggest it might not.

One reason why phrenology failed is because the method had no real scientific grounding; the same cannot be said of functional imaging. Another reason why phrenology failed was that the psychological concepts used were naïve. It is for this reason that functional imaging and other advances in neuroscience do require the insights from cognitive psychology to frame appropriate research questions and avoid becoming a new phrenology (Uttal, 2001).

The question of whether cognitive, mind-based concepts will eventually become redundant (under a reductionist account) or coexist with neural-based accounts (e.g. as in dual-aspect theory) is for the future to decide. But for now, cognitive, mind-based concepts have an essential role to play in cognitive neuroscience.

from The Student's Guide to Cognitive Neuroscience by Jamie Ward

© 2006 Psychology Press.