2018 To what extent can cognitive development be understood in terms of the specialization of function in specific structures of the brain? Developmental cognitive neuropsychology seeks to understand and explain the relationship between the human brain and its function. One might consider the extent to which cognitive development can be understood in terms of the specialisation of function in specific structures of the brain. Two contrasting theories of functional specialisation will be presented, debating the means by which brain functions develop and contesting the influence environment bears upon the maturing brain.
To enable exploration of this topic, an account of key concepts of brain development will be offered throughout. The essay will then turn to the function of language. The extent to which language is reliant upon specific cortical structures has been the subject of keen contention, and affords rich research from which to discuss whether particular regions of the brain have an innately pre-specified role to support particular cognitive functions. Research related to the prefrontal cortex will also be considered, drawing the essay to its conclusion.
To explore cognitive development in terms of the specialisation of function in specific cortical structures, one must outline association between structural differentiation and functional specialisation. The typically developed adult brain shows predictable associations between specific cortical areas with particular cognitive functions. Prior to maturation, the developing brain demonstrates increasing differentiation in both structure and function of cells, with structural changes directly affecting functional capacity.
The structural differentiation[1] of neural pathways through the processes of dendritic growth, myelination and encapsulation result in cortical areas highly efficient in supporting particular types of information, or specialised functions. The underlying reasons for the organisation of the brain in this manner are unclear. One theory seeking to explain the relationship between cortical areas and corresponding functions suggests the brain is organised into functional units, or ‘cognitive modules’. These hypothetical modules support particular functions, such as anguage, and are highly specialised to process particular information. There is significant dissent regarding the means by which development of the brain domain-specific modules occurs, centring largely on the extent to which cognitive development is genetically determined or epigenetic. The theories of two main protagonists are briefly discussed here. Fodor (1983) presents a domain-specific hypothesis of cognitive development, offering a phylogenetic viewpoint from which functional specialisation is supported by genetically determined cognitive modules – this development of the brain Fodor terms modularity.
Fodor’s theory centres on the perceptual input systems, which he proposes, process stimulus information taken from transducers, which sense stimuli, and deliver a representation of this to the central processor for higher-cognitive functions. Fodor refers to these input systems as modules, stating that the act of cognition begins at the point at which this specialised processing takes place.
Fodor states that input systems have four fundamental rudiments: they are domain-specific, each module only processing one type of information; the modules work independently of one another (encapsulation); the processing is mandatory and lastly, that input systems are rapid. Development, for Fodor, is a result of maturation, not interaction with the environment, with predetermined links between the development of specific regions of the brain with the acquisition of cognitive and motor abilities.
In contrast to Fodor, Karmiloff-Smith (1992) proposes an epigenetic theory of modularisation, in which cognitive modules develop to support specific types of information-processing as a product of the interface between genes and environment. The concept of self-organisation supports this view, proposing that the emergent neural system is marked by relative undifferentiation, but that ordered connection patterns emerge through environmental interaction.
One example of this adaptation is captured by the Hebb rule (Hebb, 1949), in which synaptic adjustment between neurons activated by environmental stimulii leads directly to lowered synaptic resistance, and thus strengthening of neural pathways. The theory of selectionism (Changeux, 1985) further supports the epigenetic argument of Karmiloff-Smith, explaining the manner by which neural pathways become specialised, with preservation of frequently used paths, whilst dendritic connections in unused-pathways die out.
Karmiloff-Smith’s principal argument for modularisation, however, relates to the flexibility of cognitive development, positing that the complexity of the human brain supports an epigenetic rationale (1992). Argument relating to brain plasticity in infants could be deemed to support this argument – whilst some brain regions are associated with particular cognitive functions, the concept of plasticity suggests the developing cortex can compensate for loss of function or damage during infancy to another cortical area[2].
Plasticity may not be epigenetic – a viewpoint exists that a determined genetic blue-print plans for the possibility of brain damage – however, the amount of encoded genetic material necessary to provide complex domain-specific functions renders epigenesis, and therefore modularisation, a more likely explanation. Having visited two opposing theoretical positions associated with cognitive development, the specialist brain function of language will be considered to illustrate the relationship between the structures and functions of the brain.
Whilst both Karmiloff-Smith and Fodor offer explanations for the key concepts of brain development outlined above, the processes of specialisation, self-organisation, and plasticity do not prove the theories of either. Research relating to the operational link between structure and function may offer resolution. Theory relating to the language function offers support to the hypothesis of modularity proposed by Fodor. The work of Chomsky (1965) put forward arguably the strongest case for genetic innateness of function, this developed further by Pinker (1994).
Pinker offers four main arguments in support of his position, which will be considered briefly. The first aspect of Pinker’s argument relates to the formation of Creoles by children raised in communities consisting of pidgin-speaking adults. Pinker refers to Bickerton, who found that children raised in migrant communities which communicated in a non-grammatically organised polyglot of dialects eventually formed their own complete Creole, including complex grammatical structures. Corresponding outcomes were evident in studies of deaf children aised by adults with non-native acquisition of sign-language, who developed grammatically-correct sign-languages. Pinker suggests that this evidences innate language instinct. Pinker’s second case relates to Chomsky’s observation on ‘the poverty of the input’, referring to abilities of children to construct grammatically-correct language despite ‘poverty’ of input. Pinker suggests the extent of input required for imitative learning of sophisticated grammatical-structures discounts the possibility of children correctly-constructing grammar based upon learning through imitation.
The third aspect of Pinker’s argument regards similarities in grammatical-structure across different languages. Pinker offers auxiliary verbs as an example, demonstrating order and grammatical rules governing use of auxiliary verbs are consistent to an extent only accountable by structural commonalities. Finally, Pinker asserts that there are specific cortical regions of the brain dedicated to language, and it is this final point which has been given significant consideration by cognitive neuropsychologists.
The principle of equipotentiality is in direct disagreement with Pinker’s nativist assertion, suggesting instead that all cortical cells begin life with ‘equal potential’ to support any aspect of function, their final role shaped by epigenetic interaction. Equipotentiality supports the argument that either hemisphere possesses the capacity to support language function, challenging the nativist case, however the research support for true equipotentiality is limited. Use of fMRI by Neville et al. (1998) to explore cortical activity during language processing found left-hemisphere activation in both hearing and deaf participants.
Additionally, deaf participants demonstrated right-hemisphere activity upon reading American Sign Language sentences, not found in hearing participants reading English sentences. Whilst right-hemisphere activity found in deaf participants might be attributed to the visual-spatial requirements of sign-language, this also suggests that areas outwith the left-hemisphere demonstrate capacity to support functions associated with processing and production of language – this offers some support to an argument of equipotentiality.
However, when considering understanding of grammatical significance and semantic words, the studies of Neville et al (1992) infer that these aspects of language processing may be more ‘innate’ than others, showing bias in specific regions for specialized function. Studies of localized brain damage in children provide further evidence that atypical cortical regions can support the function of language processing. The studies of Reilly et al. (1998) found significant deficit in language tasks amongst 3 – 9 year olds with focal lesions compared to a control group without lesions.
This longitudinal study found that children with focal lesion exhibited patterns of delayed language development, followed by a ‘catching-up’, subsequently followed by further delay at the next stage of language development. This is consistent with the concept of plasticity, suggesting that during the developmental delay new neural pathways are being established in undamaged areas to compensate for the loss of function of the lesioned area (The Open University, 2006, 17:18).
It might be argued that whilst this pattern evidences suitability of particular areas of the cortex to support specific functions, these functions can broadly be supported in other areas of the brain. The study of Stiles and Thal (1993) focussed further upon children with a focal lesion to either the left or right hemisphere. This study found that a delay in language occurred whichever hemisphere had been affected, with the group with right hemisphere lesions demonstrating greater delay in the comprehension of words.
Whilst one might expect to see this delay in adults with left-hemisphere damage, the findings suggest that the cortical areas used by children in the acquisition of language may be separate from those required for the adult processing of language – we shall revisit this concept later. The studies of Neville et al. , Reilly et al. and Stiles and Thal do not fully support either an epigenetic or a genetically-determined argument, but suggest a compromise position between.
The findings of Neville (1998) and Reilly (1998) suggest that language development can be supported by atypical cortical areas, excluding a purely nativist hypothesis given the implausibility of plural structural areas being pre-specified for one function. The findings of Reilly et al. (1998), however, support the concept of cortical areas having predisposition for the support of language. Whereas genetic constraints are suggested by the developmental delay demonstrated by Reilly et al. the brain demonstrates ability to self-organise in interaction with environment. Considering further the relationship between emerging brain structures and functional maturation, one might explore the role of the prefrontal cortex. Responsible for executive functions (Milner, 1982; Goldman-Rakic, 1987; Fuster, 1989), the pre-frontal cortex shows significant postnatal development, experiencing greater environmental stimulii than other cortical regions, associating this region particularly with cognitive development.
Opposing theories debate the role of this region; the first stating cognitive development is directly associated with structural development in this area (Diamond and Goldman-Rakic, 1989), the second that the prefrontal cortex offers an organisational role in the acquisition of new skills, its involvement decreasing as the function is mastered and supported by a specialised cortical region (Johnson et al, 1998; Csibra et al, 1998).
Whilst studies of damage to language function suggests cognitive development to be wholly domain specific, research related to damage to the pre-frontal cortex supports the notion that some areas of the brain offer domain-general functions (Shallice, 1988). Studies related to the prefrontal region uphold a relationship between developing cortical structure and the emergence of functional ability and suggest adult cognition to largely be modular, yet challenges the notion of cognitive modules as independent and domain-specific in nature.
To conclude, study of specialization of function in specific structures of the brain offers significant insight into cognitive development. Whilst the exact relationship between development of brain structure and specialisation of function remains indefinite, hypotheses for the organisation of the brain into functional modules offer credible explanations for how this process might occur, with research offering some support to both epigenetic and nativist positions presented.
Whilst studies of language demonstrate predisposition in specific structures for the support of this specialized function, the typical cortical region was demonstrably not critical for language production. Genetic material clearly places constraints upon development, however studies of plasticity show the capacity of the brain to self-organise in interaction with environment. The above suggests that cognitive development is largely epigenetic and modular in nature, with different cognitive modules performing specific and highly independent functions.
Research concerning the role of the pre-frontal cortex, however, presents a compelling argument for reconsidering this pleasingly simplistic notion of development. This suggests that the domain-specific specialization of function suggested by studies of language may not be comprehensively applicable, with other aspects of the brain having an organisational role in the acquisition of new functional skills. References Changeux, J. P. (1985), cited in Mareschal et al (2004) p. 124. Chomsky, N. (1965), cited in Mareschal et al (2004) p. 135, 137. Csibra, G. , Tucker, L. A. nd Johnson, M. H. (1998), cited in Mareschal et al (2004) p. 148. Diamond, A. and Goldman-Rakic, P. S. (1989), cited in Mareschal et al (2004) p. 146. Fodor, J. A. (1983), cited in Mareschal et al (2004) p. 127-128. Fuster, J. M. (1989), cited in Mareschal et al (2004) p. 145. Goldman-Rakic, P. S. (1987), cited in Mareschal et al (2004) p. 145. Hebb, D. (1949), cited in Mareschal et al (2004) p. 133. Johnson, M. H. , Tucker, L. A. , Stiles, J. and Trauner, D. (1998), cited in Mareschal et al (2004) p. 148. Karmiloff-Smith, A. (1992), cited in Mareschal et al (2004) p. 29. Mareschal, D. , Johnson, M. H. and Grayson, A. (2004) ‘Brain and Cognitive Development’, in Oates and Grayson (eds) Cognitive and Language Development in Children, Oxford, Blackwell/The Open University. Milner, B. (1982), cited in Mareschal et al (2004) p. 145. Neville, H. J. , Bavelier, D. , Corina, D. et al. (1998), cited in Mareschal et al (2004) p. 139. Neville, H. J. , Mills, D. and Lawson, D. (1992), cited in Mareschal et al (2004) p. 140. Pinker, S. (1994), cited in Mareschal et al (2004) p. 135-8. Reilly, J. S. , Bates, E. A. and Marchman, V.
A. (1998), cited in Mareschal et al (2004) p. 140-142. Shallice, T. (1988) ‘Reading B: Beyond Modularity’, in Oates and Grayson (2004) p. 158-161. Stiles, L. and Thal, D. (1993), cited in Mareschal et al (2004) p. 142. The Open University (2006) ‘Video Band 6: Finding a Voice: Alex and Leigh,’ Media Kit Part 3, ED209 Child Development DVD-ROM, Milton Keynes, The Open University. ———————– [1] Increased dendritic growth and resultant synaptic connectivity in a particular neural pathway increases its facility to transmit electrical activity.
Increased myelination, or insulation, of the developed neural pathway further hastens transmission. Additional to the insulating effects of myelination, the decreased number of nerve cell connections characteristic of latter stages of brain development reduce neuronal connections between pathways, resulting in an encapsulated system closed off from other pathways. [2] Plasticity is only possible during maturation, after which the cells and tissues of the neural pathway are too differentiated and encapsulated to alter their form or function significantly.
