Sunday, October 23, 2005

Speaking of (autistic) brains...   posted by Theresa @ 10/23/2005 03:09:00 PM

Dr. Manuel Casanova has done some interesting research on neuronal minicolumns and autism. From the summary of Abnormalities of Brain Circuitry (Minicolumns) in Autism:

[The] neocortex is formed early on during gestation by the supernumerary aggregation of modules. The smallest module capable of processing information is called minicolumns. These modules or minicolumns are composed of both cells (neurons) and their projections which together form standardized circuits. Recent studies suggest that minicolumns may be abnormal in autism. More specifically, the brains of autistic patients have minicolumns that are smaller and more numerous than normal. Furthermore, the cells (neurons) within each minicolumn are reduced in size.

Since the metabolic efficiency of neuronal connectivity is a function of cell size, the presence of smaller neurons in the brains of autistic patients has a dramatic effect on the way that different parts of the brain interact with each other. Functions that require longer projections (e.g., language) may be impaired while shorter ones (e.g., mathematical manipulations) may be preserved or reinforced.


In autism, smaller minicolumns in brains that are, on average, larger than normal suggests their total increase in numbers....

What is the meaning of smaller minicolumns? First, this question has been approached from the standpoint of computer modeling by a group in Switzerland (Dr. Gustafsonā€™s). Results suggest that smaller minicolumns tweak information processing in favor of the signal. By comparison other conditions characterized by larger minicolumns (e.g., dyslexia) tweak information processing in favor of noise. This means that autistic individuals usually do well in processing stimuli that requires discrimination while dyslexics are better at generalizing the salience of a particular stimulus.

Second, minicolumns are compartmentalized. Information is transmitted through the core of the minicolumn and is prevented from suffusing into neighboring units by surrounding inhibitory fibers. The inhibitory fibers act in analogous fashion to a shower curtain. When working properly and fully draping the bathtub the shower curtain prevents water from spilling to the floor. In autism minicolumnar size reduction involves primarily the peripheral compartment that provides the inhibitory surround.

This means that stimuli are no longer contained within specific minicolumns. Stimuli overflow to adjacent minicolumns thus providing an amplifier effect. This may explain the hypersensitivity of some autistic patients as well as their seizures....

Minicolumnar size is not the only abnormality observed in the neocortex of autistic patients. It appears that cells (neurons) within individual minicolumns are also reduced in size. This has important consequences in terms of connectivity. Long connections require the metabolic sustenance of large cell bodies. A neuron in the brain that connects all the way to the lower spinal chord requires a fairly large cell body. By way of contrast, a neuron whose projection remains within the cortex, contacting a closely adjacent cell, can manage its metabolic demands with a small cell body.

The small cell bodies in the brains of autistic patients favor information processing through short intra regional pathways, e.g., mathematical calculations, visual processing. Similarly, cognitive functions that require long inter regional connections would prove metabolically inefficient, e.g., language, face recognition, joint attention.

More on autistic brains: The essential difference and Male brain ~ more sons vs. female brain ~ more daughters?

More on minicolumns: The minicolumn hypothesis in neuroscience