REVIEW

TRANSFORMATIONS OF POLYNESIAN CULTURE. Edited by Antony Hooper and Judith Huntsman. Auckland: The Polynesian Society. 1985. Pp. 226. Price: $NZ 35. (paper).     

Stone Tool-Making and Brain Activation: Position Emission Tomography (PET) Studies

This study introduces to archaeology a new experimental technique for examining the relationship between stone tool-making and brain function. The principal focus of this exploratory study was the development of effective methods for the identification and examination of the regions of the modern human brain recruited during the manufacture of simple (Oldowan or Mode I) stone tools. The functional brain imaging technique employed, Positron Emission Tomography (PET), examines task-related brain activity by assessing changes in regional cerebral blood flow during specific tasks. The single-subject study reported here represents a heuristic, initial exploration of this subject. Results indicate that during stone tool-making there was heavy activation of cortical and subcortical regions of the brain associated with motor and somatosensory processing. Especially interesting was the high degree of activation in areas known to be involved with complex spatial cognition requiring integration of diverse sensory inputs (e.g. vision, touch, and proprioception, or sense of body position and motion). Expansion of such higher-order association areas has been particularly important during the course of human evolution. This single-subject pilot study demonstrates the application of the PET brain imaging technique to the study of early stone technologies and suggests hypotheses to be tested in more comprehensive studies in the future.     

Mechanisms of fluid flow and fluid–rock interaction in fossil metamorphic hydrothermal systems inferred from vein–wallrock patterns, geometry and microstructure

Comparison of mass transfer patterns, geometry and microstructures developed within and around veins allows the interpretation of processes of fluid flow during deformation, metamorphism and mineralization. A classification of vein types based on the degree of interaction with wallrock (using petrological, geochemical or isotopic indicators) can be used to identify a range of processes, from closed system behaviour in which the vein mass is derived from local wallrock, through to open system behaviour in which the vein mass is derived externally. Microstructural characteristics, such as wallrock selvages, multiple growth events recorded by vein seams and vein crystal morphology, also help to constrain mass transfer patterns during vein formation. We present a range of processes for vein formation, including: (i) the formation of closed system fibrous veins by dissolution–precipitation creep, including varieties in which tensile failure is not required; (ii) pressure‐ or kinetically dependent closed system segregation veins in which transfer of soluble components from wallrock to vein leaves behind a residual selvage; (iii) similar vein–selvage patterning, but with mass imbalances between vein and wallrock requiring fluid advection through both interconnected fracture networks and in the surrounding permeable rock; and (iv) the proposed formation of veins by fluid ascent in mobile hydrofractures, in which isotopic or chemical disequilibrium within and around the vein suggests that the crack and fluid within it moved essentially as one. The postulate of rapid fluid and mass transfer via such mobile hydrofractures has implications for the release of volatiles from metamorphic terrains. Also, consideration of a broad range of possible vein‐forming mechanisms is highly desirable when dealing with mineral deposits found in deformed, metamorphosed rocks, because closed system veining may produce patterns that, if erroneously recognized as being open systems, could lead to false interpretations of the role of tectonic fracturing in ore genesis.