Top-Down Attentional Control of Visual-Processing

Attention is required for most, if not all, perceptual processes. There is a converging body
of evidence from single-cell recording studies in monkeys and neuroimaging, behavioral, and
clinical studies in humans showing that the processing of attended information is enhanced
relative to the processing of unattended information.

What is the source of this attentional modulation? Because neuroimaging studies have
demonstrated that multiple cortical regions are recruited during tasks involving selective
attention, it has proven difficult thus far to determine the differential contributions of
each region. A central goal of the proposed research is to characterize the contributions of
prefrontal cortex and parietal cortex and test the hypothesis that these regions exert
top-down modulatory influences over visual processing areas. Specifically, we wish to
investigate the interaction between areas involved in attentional control and visual areas
modulated by attention.

We propose to study patients with focal lesions and healthy volunteers while they perform
tasks requiring attention. Subjects will participate, first, in a series of behavioral
studies involving selective attention; the relative performance of different patient groups
and neurologically healthy volunteers will be compared. Subjects will also be studied while
performing similar tasks during functional magnetic resonance imaging (fMRI). We hypothesize
that selective attention will be heavily impaired by lesions of key prefrontal (e.g.,
dorsolateral prefrontal cortex) and key parietal (e.g., superior parietal lobule) sites. We
also expect that brain imaging data will show decreased activation in visual regions
ipsilateral to the focal lesions in prefrontal and parietal cortex, thus providing evidence
that prefrontal and parietal cortex are sources of top-down modulation. Although other
research groups have compared the behavior of patients with various focal lesions or have
performed fMRI studies of visual attention in neurologically normal patients, we are unaware
of any concerted effort to perform fMRI in patients with focal lesions in order to
functionally isolate the contributions of individual cortical regions that serve as critical
nodes in the attentional network.

- INCLUSION CRITERIA:

All Subjects

1. All subjects will be 18 years of age or older and have at least a high school
education.

2. Capacity to provide their own informed consent, understand and cooperate with study
procedures.

Patients:

1. Unilateral or bilateral focal lesions of prefrontal, parietal, occipital or temporal
cortex, or amygdala.

2. At least three months post-stroke, lobectomy and or neurosurgical resection.

Healthy volunteers:

1. Neurologically normal and in good general health.

EXCLUSION CRITERIA

Patients:

1. Any neurological or psychiatric disorder not related to the focal lesion (e.g.,
epilepsy, schizophrenia, etc.). Epilepsy patients who have undergone surgery and as a
result are seizure free may be recruited.

2. Previous head injury.

3. Present or past (within past 6 months) drug or alcohol abuse or addiction as
determined by a qualified study neurologist/psychiatrist.

4. Radiation treatment to the brain during a three-month period prior to the experiment.

5. NIMH staff and their immediate family are excluded from participation.

Healthy Volunteers:

1. Any neurological or psychiatric disorder (e.g., epilepsy, schizophrenia, etc.)

2. Previous head injury.

3. Present or past (within past 6 months) drug or alcohol abuse or addiction based on
DSM-5 criteria as determined during History and Physical exam.

4. NIMH staff and their immediate family are excluded from participation.

ADDITIONAL EXCLUSION CRITERIA FOR MRI SCAN:

Patients and Healthy volunteers:

1. Women who are pregnant and women of child-bearing potential who refuse to undergo a
urine pregnancy test will be excluded from fMRI experiments but included in cognitive
experiments.

2. Subjects who have contraindications to MRI scanning will be excluded from FMRI
experiments but included in cognitive experiments. These contraindications include:

1. central nervous system aneurysm clips;

2. implanted neural stimulator;

3. implanted cardiac pacemaker or defibrillator;

4. cochlear implant;

5. ocular foreign body (e.g., metal shavings);

6. insulin pump;

7. metal shrapnel or bullet;

8. any implanted device that is incompatible with MRI.

3. Conditions that preclude scanning, e.g., morbid obesity, claustrophobia.

ADDITIONAL EXCLUSION CRITERIA FOR TASKS INVOLVING COLOR DISCRIMINATION:

Patients and Healthy volunteers:

Subjects who are determined during screening or history and physical exam to be color-blind
will be excluded from participating in certain tasks that involve color discrimination.