|
This study aims to determine whether the cerebellum
usually linked to motor control may play a role in executive functioning.
Clinical studies of patients with diseases confined to the cerebellum
suggest that the cerebellum is involved in higher cognition. In
this study the CSST will be used to assess the executive function
of rhesus monkeys with cerebellar lesions. If these monkeys show
significant impairment in executive function then the cerebellum
(in addition to the prefrontal cortex) may be a target for age-related
decline.
Researchers have used the CSST to assess executive function in rhesus
monkeys and have shown that aged monkeys like aged humans evidence
a decline in executive functioning which includes such abilities
as abstraction maintenance of set shifting of set and cognitive
flexibility.
Subjects: 7 male rhesus monkeys; 3 of these monkeys have lesions
of the cerebellum & 4 are normal controls.
Of this group all of the control monkeys and 2 of the cerebellar
monkeys have been previously tested on the CSST Shaping Task: A
pretraining task was used to teach each monkey to touch the computer
screen which required the monkey to touch a single stimulus on the
screen to receive an M&M reward. The stimulus then appeared
in random locations on the screen.
Selected Task: After shaping the monkeys begin the CSST task. Each
trial of the CSST will present the monkey with three stimuli on
the touchscreen that differ in color and shape. Initially the monkey
must use the dimensions of color (red) to identify the correct stimulus.
After the monkey responds correctly on 10 consecutive trials the
reward contingency shifts so that the relevant dimension is shape
(triangle) which is rewarded regardless of color. An initial acquisition
and three shift conditions will be administered (red triangle blue
star).
The monkeys with cerebellar lesions show impairment in acquisition
of the first set and all three set shifts of the CSST. The cerebellar
monkeys frequently make perseverative errors on the CSST by choosing
the correct stimulus from the prior set.
As shown by the data monkeys with cerebellar lesions are noticeably
impaired on the CSST which tests executive function. These preliminary
results encourage this study to complete the CSST testing on the
three cerebellar monkeys. The larger sample size of lesioned monkeys
will allow for future tests of significance against the controls.
If future results show that monkeys with cerebellar lesions are
significantly impaired in executive function then the cerebellum
must play a role in higher cognition and may be a target for age-related
decline.
1. Herndon JG, Moss MB, Rosene DL, Killiany RJ. Patterns of cognitive
decline in aged rhesus monkeys. Behav Brain Res 1997; 48: 148-53.
2. Moore TL, Killiany RJ, Rosene DL, Moss MB. Lesions of dorsal
prefrontal cortex produce an executive function deficit in the Rhesus
monkey. Soc Neurosci Abstr 2001; 31.
3. Moore TL, Killiany RJ, Herndon JG, Rosene DL, Moss MB. Impairment
in abstraction and set shifting in aged Rhesus monkeys. Neurobio
and Aging 2003; 24: 125-134.
4. Schmahmann JD and Sherman JC. The cerebellar cognitive affective
syndrome. Brain 1998; 121: 561-579.
Supported by Howard Hughes Medical Institute and NIH grants RR00165
and AG00001
The cerebellum is a brain region that has always been thought to
control motor functions. However the cerebellum may also play a
role in higher cognition such as executive functioning which enables
us to have cognitive flexibility. For example, Australians drive
on the left side of the road. If you are walking across the street
in Australia you would use your executive functioning to look right
before crossing even though you are used to looking left. In order
to test this hypothesis my study tested Rhesus monkeys with lesions
in their cerebellum to see if they would do worse on a computer
task that requires executive functioning. The preliminary results
suggest that these lesioned monkeys are impaired on the task.
|
