Functional anatomy of the brain

Basic Functional Anatomy of

Functional neuroimaging of the brain, in both humans and other species, continues to provide crucial insights into structure–function relationships across a wide range of cognitive, affective and praxic capacities. These new techniques of in vivo measurement of local blood flow, in response to neuronal demand within the brain, complement the classic anatomical–clinical method in which the behavioural consequences of cerebral lesions (following accidents of nature or experimental ablations) are investigated. In particular, positron emission tomography (PET) and functional magnetic resonance imaging (fMRI) allow us to correlate increases in neuronal activity in specific brain regions and circuits contingent upon well-defined sensory inputs, the performance of particular cognitive tasks, and appropriate response by distinct motor systems.

An impression of the scope of current work can be gained from the three reviews that follow. The paper by Christian Grefkes and Gereon Fink is set in an evolutionary context. Many (but not all) of the spatial problems that macaque monkeys and humans must solve in order to cope in a three-dimensional world are held in common; it is thus likely that many (but not all) of the functionally relevant brain areas in the posterior parietal cortex are fairly well preserved across the two species. Grefkes and Fink compare and contrast the structural and functional anatomy of the interparietal sulcus (IPS) in macaque and human, showing that particular regions along the sulcus are responsible for distinct visuospatial, visuomotor and attentional processes in both species, although there may be more functionally specialized visuospatial areas in human IPS than in monkey IPS. Disproportionate expansion of cortical regions in humans has also led to differences in the anatomical arrangement of functionally defined areas in the two species. Their paper clearly illustrates how the different techniques appropriate to investigating cortical function in these two species (electrophysiological recording from single cells in macaques; fMRI; and the study of neurological impairments after stroke in humans) can illuminate our understanding of a generic problem.

The review of the functional anatomy of pain by Jonathan Brooks and Irene Tracey shows how far we have advanced since the 17th century in our understanding of the brain's response to noxious stimulation. For Descartes, particles of fire (for example) displaced the area of skin they touched, which in turn pulled on a ‘thread’ running along the peripheral nervous system to its termination in the brain. Here the thread pulled open the ‘conduit’ to the cerebral area responsible for feeling pain. By contrast, Brooks and Tracey can show that different classes of afferent peripheral nerve fibres convey information about different types of pain, and that several distributed brain regions (not solely the primary somatosensory cortex, S1) are active during painful stimulation. In particular, one can distinguish between a medial and a lateral pain system in the cortex; based on projections from the medial and lateral thalamus. The lateral system, based on primary and secondary somatosensory cortex (S1 and S2), conveys the location and intensity of painful stimulation, while the medial system, based on anterior cingulate cortex (ACC), codes affective and evaluative aspects of pain (why pain feels painful). This medial system is activated by empathic observation of another's pain, and by the pain of social exclusion. The ultimate aim of pain research is, of course, to ameliorate chronic pain. Here functional neuroimaging studies are beginning to explore how brainstem structures are involved in the descending control of pain via connections to the spinal cord dorsal roots.

Morris Moskovitch and colleagues show how functional neuroimaging, in conjunction with lesion studies, can elucidate the neuronal bases of three distinct types of memory, (a) episodic memory in which particular autobiographical events from one's relatively remote past must be retrieved; (b) semantic memory, in which particular facts must be retrieved (e.g. Paris is the capital of France), irrespective of how, when, why or where the information was acquired; and (c) spatial memory, including information about what is where and how to get there. The ‘knowledge’ of experienced London taxi-drivers draws extensively upon this third type of memory. Moskovitch and colleagues argue that the hippocampus is the crucial structure implicated in the retention and retrieval of remote and recent memories that are vivid, detailed autobiographical episodes. The hippocampus, they claim, allows us to re-experience our past; it plays a role in semantic and spatial memory insofar as these memories have an episodic, experiential character. But when semantic and spatial memory becomes more schematic, more a set of propositions than a personal experience, then neocortical regions, including the temporal and parietal lobes, can preserve the information even in the face of extensive hippocampal lesions.

These three articles arose from a symposium of the Anatomical Society of Great Britain and Ireland entitled ‘Functional anatomy of the human brain’, held in London in January 2004. Three other articles from this symposium, by K. Zilles et al., U. Noppeney et al. and K. E. Stephan, were published in the December 2004 issue of Journal of Anatomy (Vol. 205, issue 6), which can be accessed free on .

The cover of this issue of the journal highlights the continuity between the 17th century insights of Descartes and 21st century fMRI in understanding the perception of pain.

You might also like

Super computers to map the human brain
Super computers to map the human brain
Sound maps of the human skull will enable new, noninvasive
Sound maps of the human skull will enable new, noninvasive ...
New Study Maps the Highways of the Brain
New Study Maps the Highways of the Brain
Allan Jones: A map of the brain
Allan Jones: A map of the brain

Copyright © . All Rights Reserved