Updated September 15, 2003.
Patients with chronic alcoholism develop a wide range of brain structural and neuropsychological abnormalities. Deficits in executive functioning - such as problem solving, putting things in order, working memory, and doing multiple tasks at once - have been linked to lesions of the prefrontal cortex. Deficits in balance have been linked to lesions of the cerebellum.
A study in the September 2003 issue of Alcoholism: Clinical & Experimental Research has found that the circuitry connecting these two spatially disparate brain regions, specifically through the pons and thalamus, may allow lesions to compound their effects on the prefrontal cortex and cerebellum.
"Neuropathological, neuroimaging, and neuropsychological studies have shown that the prefrontal cortex and regions of the cerebellum are especially vulnerable to the untoward effects of chronic alcoholism," said Edith Sullivan, a professor in the department of psychiatry and behavioral sciences at Stanford University School of Medicine and the sole author of the study.
"Other neuroscience research provides evidence that, despite their geographical distance in the brain, the prefrontal cortex, which is at the frontal lobe, and the cerebellum, which is basically the hindbrain, are connected by far-reaching white matter tracts and a structural neural network. It seemed very likely that damage to one node or individual brain structure of this frontocerebellar system could affect other nodes within that circuitry, both structurally and functionally."
Sullivan chose to examine two major circuits of the frontocerebellar system, the pons and the thalamus. Information flows from the frontal cortex through the pons to the cerebellum; information also flows from the cerebellum through the thalamus to the frontal and parietal cortices.
Sullivan used magnetic resonance imaging (MRI) to derive regional brain measures from 25 nonamnesic alcoholic men. Control data were obtained from an age-matched group of 51 men. Previous results had revealed significant volume deficits among the alcoholics in the cerebellar hemispheres and vermis, pons, and thalamus as well as the prefrontal, frontal, and parietal cortex. These same individuals also demonstrated deficits in problem solving, visuospatial ability, and static postural stability. The purpose of this study was to closely examine associations among target brain volumes and neuropsychological deficits.
"We knew that various nodes that comprise the frontocerebellar networks show volume shrinkage in patients with chronic alcoholism," said Sullivan. "Such dysmorphology puts these individuals at risk of deficits in functions subserved by these brain structures. Given this background, we examined the relationship between brain volumes of the circuit nodes and observed that nodes that are known from animal studies to be highly connected also showed correlations in their volume measures."
"Pontine and thalamic volumes were not correlated with each other," Sullivan continued. "Pontine volumes correlated with white matter volumes of key regions of the cerebellum but not of the cortex. Thalamic volumes correlated with gray matter volumes of the cerebellum as well as certain regions of the cortex, including the parietal lobes, and inferior posterior vermian lobule, which itself correlated with parietal, prefrontal and frontal cortex volumes. These patterns of correlations were consistent with the separation of thalamic and pontine subcircuitry of the greater frontocerebellar circuit."
Part Two: 'Executive' Functions Disrupted
Patients with chronic alcoholism develop a wide range of brain structural and neuropsychological abnormalities. Deficits in executive functioning - such as problem solving, putting things in order, working memory, and doing multiple tasks at once - have been linked to lesions of the prefrontal cortex. Deficits in balance have been linked to lesions of the cerebellum.
A study in the September 2003 issue of Alcoholism: Clinical & Experimental Research has found that the circuitry connecting these two spatially disparate brain regions, specifically through the pons and thalamus, may allow lesions to compound their effects on the prefrontal cortex and cerebellum.
"Neuropathological, neuroimaging, and neuropsychological studies have shown that the prefrontal cortex and regions of the cerebellum are especially vulnerable to the untoward effects of chronic alcoholism," said Edith Sullivan, a professor in the department of psychiatry and behavioral sciences at Stanford University School of Medicine and the sole author of the study.
"Other neuroscience research provides evidence that, despite their geographical distance in the brain, the prefrontal cortex, which is at the frontal lobe, and the cerebellum, which is basically the hindbrain, are connected by far-reaching white matter tracts and a structural neural network. It seemed very likely that damage to one node or individual brain structure of this frontocerebellar system could affect other nodes within that circuitry, both structurally and functionally."
Sullivan chose to examine two major circuits of the frontocerebellar system, the pons and the thalamus. Information flows from the frontal cortex through the pons to the cerebellum; information also flows from the cerebellum through the thalamus to the frontal and parietal cortices.
Sullivan used magnetic resonance imaging (MRI) to derive regional brain measures from 25 nonamnesic alcoholic men. Control data were obtained from an age-matched group of 51 men. Previous results had revealed significant volume deficits among the alcoholics in the cerebellar hemispheres and vermis, pons, and thalamus as well as the prefrontal, frontal, and parietal cortex. These same individuals also demonstrated deficits in problem solving, visuospatial ability, and static postural stability. The purpose of this study was to closely examine associations among target brain volumes and neuropsychological deficits.
"We knew that various nodes that comprise the frontocerebellar networks show volume shrinkage in patients with chronic alcoholism," said Sullivan. "Such dysmorphology puts these individuals at risk of deficits in functions subserved by these brain structures. Given this background, we examined the relationship between brain volumes of the circuit nodes and observed that nodes that are known from animal studies to be highly connected also showed correlations in their volume measures."
"Pontine and thalamic volumes were not correlated with each other," Sullivan continued. "Pontine volumes correlated with white matter volumes of key regions of the cerebellum but not of the cortex. Thalamic volumes correlated with gray matter volumes of the cerebellum as well as certain regions of the cortex, including the parietal lobes, and inferior posterior vermian lobule, which itself correlated with parietal, prefrontal and frontal cortex volumes. These patterns of correlations were consistent with the separation of thalamic and pontine subcircuitry of the greater frontocerebellar circuit."
Part Two: 'Executive' Functions Disrupted