femme Neuroscience Notes

Some Topics

The Brain

The brain is the organ of the mind. Anatomists have described the brain in terms of our evolutionary path. We have old-age, middle-age and new-age parts, each with different properties. A neuroscientist, Paul McLean, suggested that the human brain could be viewed as three systems of different ages - an old reptilian brain, a middle (early mammalian) brain, topped off with a new, advanced brain, the neocortex.

The neocortex has the computer equivalent of random access memory (RAM), allowing the input of new information  This new information is used to interpret and adjust the operation of read-only memory (ROM) which is built into old and middle brain modules and cannot be modified. New babies are not born with the new brain programs. Old programs are built into us and need not be learned. Old programs include some of the most negative qualities – predatory and territorial aggression, anger and fighting, for example. Some of our most positive qualities are also innate such as the tendencies to mate, bond and form social units with altruistic features. The old brain remains in control of our bodies and our minds.

An essential feature of a brain is the ability to tune into what is ongoing on out there using a variety of input devices. Tuning is not a feature of digital computers but is found in all radio communications. An old radio set with a tuning knob is a good place to start when you want to understand brain function. There is a range of electromagnetic frequencies broadcast in the universe, involving a range of energies. The animal brain tunes into a small range of highly selected frequencies and extracts data from this continuous and prolific stream of information.

Science has advanced by inventing devices, optical and electronic, that extend our ability to sense this wave information. We have invented devices that can tune into every known electromagnetic frequency and we detect photons as particles that expose film and activate photon-energy-sensitive electronic detectors. Our ability to magnify and amplify events in an otherwise unseen microcosm is the foundation of science and technological advances. All our marvelous devices are extensions of our native ability to sense what is going on out there.

Tuning in the brain involves clusters of processors for every sensory system. Careful studies of the visual cortex, for example, have revealed clusters of highly specialized cells that detect single features. Discrete columns of specialized neurons respond as if they were programmed to deliver specific information such as <column 1 - detect all edges moving to the left>. The combination of tuning circuits extracting specific information (focal awareness) with a scanning, broadband information seeker (global awareness) appear to be the basic plan of interaction with the outside world.

Brain mapping using functional magnetic resonance imaging (fMRI) reveals complex assemblies of cortical processors that are specialized to individual tasks. The recognition of visual objects, for example, is assigned to different domains for different classes of objects.

Ishai and colleagues  described specialized cortical areas for the recognition of pictures of faces, houses and chairs:  “Recently, we identified, using fMRI, three bilateral regions in the ventral temporal cortex that responded preferentially to faces, houses, and chairs …Here, we report differential patterns of activation, similar to those seen in the ventral temporal cortex, in the bilateral regions of the ventral occipital cortex. We also found category-related responses in the dorsal occipital cortex and in the superior temporal sulcus. Moreover, rather than activating discrete, segregated areas, each category was associated with its own differential pattern of response across a broad expanse of cortex. The distributed patterns of response were similar across tasks (passive viewing, delayed matching) and presentation formats (photographs, line drawings). We propose that the representation of objects in the ventral visual pathway, including both occipital and temporal regions, is not restricted to small, highly selective patches of cortex but, instead, is a distributed representation of information about object form. Within this distributed system, the representation of faces appears to be less extensive as compared to the representations of non-face objects. “