Grey Matters: Glimpsing the Grey Marble



Quiet as an eyeblink clicked the camera shutter from the window of Apollo 17.  Astronauts Cernan, Evans, and Schmitt on December 7, 1972 captured the first clear and fully illuminated image of Earth ever taken from space.  This historic and widely circulated “Blue Marble” photograph of our fragile globe, depicted in vibrant blue, green and white and suspended in the vast blackness of silent space, has stirred the imagination of a generation. 

Having glimpsed the Earth as a whole, the way we think about our world is forever changed.  Now we have seen the Blue Marble and recognize it as our common home.  Viewed from space, no political, military, racial or linguistic divisions disrupt its contours.  Planet Earth is one world and a shared habitat.  All who dwell on the geologic wrinkles of its rotating topography belong to a global community. 

Earth is also a special home.  No other known planet’s surface temperature is so finely tuned that water can exist in its threefold phases of ice, liquid and gas.  Plentiful water, sunlit and tranquil, gives Earth its distinctive celestial beauty.  In years past, only portions were visible from the surface.  Seen from space, the full expanse of gleaming glacial shelves, deep blue oceans’ shimmering waves, and cumulus clouds’ soaring swirls all burst into brilliant view. 

From space one can also appreciate that planet Earth is a vulnerable milieu.  Its life-giving atmosphere delicately clings to the globe as a thin rim insulating its surface from the void beyond.  Rivers flow as tiny bright trickles.  Mossy forests’ margins dwindle.  Fertile plains extend to finite borders.  Natural resources that seem, from the surface perspective, to stretch as far as the eye can see are, from the vantage point of space, precious and limited and not to be taken for granted.  The awe-inspiring Blue Marble image fosters a sense of shared responsibility. 

Another historic image acquired from an orbiting perspective is transforming our mental view of human nature.  1972 was also the year that Hounsfield and Cormack invented computed tomography (CT), for which they were later awarded the Nobel Prize.  Its first medical application was to acquire images of the human brain.  The patient undergoing a CT scan lies motionless on a table within a doughnut-shaped tube, while a beam-emitting x-ray tube and corresponding detector rapidly encircle the body, gathering a series of images from sequential angular positions.  In this way the CT generates cross-sectional representations, or slices, of human anatomy.  CT provided the first clear and anatomically detailed images of the living human brain.  All the gyral folds of grey matter previously hidden beneath the skull have come into splendid view, arrayed in shades of digital grey on the computer display. 

This “Grey Marble” image of the human brain is increasingly capturing the imagination of humanity.  Images of the human brain now abound in a world that ponders what neuroscience is revealing about the three pounds of neural tissue that reflects on the origin and purpose of itself and the universe. 

Whereas there is one image bearing the name Blue Marble corresponding to the one Earth, there are in medical clinics worldwide multitudes of Grey Marble images representing just a fraction of the billions of people inhabiting the Earth.  Grey Marble images lack sufficient detail to show individual particularities and do not distinguish among differences in gender, ethnicity, language or nationality.  The Grey Marble is thus a fitting portrait of our shared human cognitive nature.  Yet we also know that each brain is biologically and biographically unique and that every person is special.

Viewed as a whole, a number of features of the Grey Marble stand out.  The frontal, temporal, parietal and occipital lobes are not physically disconnected as are earthly continents but merge one into another.  While each cortical area has its own specific function, brain regions are also integrated and interactive.  The dynamic behavior of widely distributed neural fields compose the neural correlates of consciousness.  This intangible quality of self-awareness still eludes full explanation by neuroscience, for the subjective and the spiritual aspects of life encounter a dimension of reality as imperceptible to empirical investigation as is wind to the camera.  Words, like clouds, briefly outline their direction, and then fade away.  Within the brain, streams of thought meander through unanticipated contemplative terrain.  Seasons of passion and lassitude come and go.  Ideas sail the seas of surging neurochemistry, while emotions keep their curious ebb and flow.  Within this paradoxical seat of human intelligence coexist the potential for stormy anger and gracious kindness.  And at each extreme of polarized debate lie accretions of icy obstinacy.

The Blue Marble has aroused an ethic of ecology concerned with the responsible use and preservation of Earth’s natural resources.  Environmental awareness extends also to the brain, for it matters what kind of thoughts we choose to fill our brains with.

Wrapped within the Grey Marble is a world of ideas.  Just as planet Earth is home to complex ecosystems hosting amazing diversity of life not easily visible from space, the brain is far more complex and subtle than whole brain imaging studies can represent.  The Grey Marble is emblematic of interconnectedness.  Each of its hundred billion neurons has, on average, 3000 synaptic connections with other neurons.  Some individual neurons receive as many as 150,000 contacts.  A cubic millimeter of cerebral cortex contains about a billion synapses.  When disease severs those connections and neurons fail to communicate with one another, the brain functions poorly.  Visualizing the brain as a whole evokes an understanding of intelligence consisting of a variety of cognitive functions combined into a community of thoughts.  The brain is a unit, though it is made up of many parts, and though all its capacities are many, they form one mind.  Hence when reason conflicts with intuition in grappling with an ethical dilemma, all the brain’s resources are needed to discover wisdom.  Just as humble microorganisms are essential to healthy flourishing of advanced life on Earth, even the pathways in the brain that seem to be weaker are indispensable.  If one part suffers, the whole brain suffers with it.  The fusiform gyrus needs the calcarine cortex.  The prefrontal cortex needs the amygdala.

There are limits to what images can convey.  Although digital technologies are reconstructing images of the Earth and of the brain in progressively finer detail, it must be remembered that, just as pictures of Earth from space detect only its surface, images of the brain visualize only its material nature.  Moreover, at any given time, the Blue Marble is only half a picture of planet Earth.  The brain, too, has its bright side and its dark side.

These wondrous marble images are reminders that the Earth, its inhabitants, and its minds are gifts and not things of our own making.  How their images are rendered, whether as dull or vivid, affirming or dismissive, cynical or hopeful, will shape how our culture thinks about human cognitive nature from its tenuous beginning to its earthly end. 

Through scans we perceive the grey matter as in a mirror dimly.  Nevertheless, the human mind open to the light of truth shines with rainbows of understanding, thanksgiving and blessing.  The full potential of the human mind can be realized once the brain is full of the knowledge of the LORD as the waters cover the sea.


Editor's Note: The views expressed herein are Dr. Cheshire's own and do not necessarily reflect the positions of Mayo Clinic or Mayo Foundation, USA. This article originally appeared in Ethics & Medicine: An International Journal of Bioethics 23, no. 2, (2007) and is used with permission.


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