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

• All subjects will be 18 years of age or older and have at least a high school education.
• Capacity to provide their own informed consent, understand and cooperate with study procedures.
• Able to read and write in English to guarantee understanding of all written and spoken instructions, which are in English.

Patients:

• Unilateral or bilateral focal lesions of prefrontal, parietal, occipital or temporal cortex, or amygdala.
• At least three months post-stroke, lobectomy and or neurosurgical resection.

Healthy volunteers:

• Neurologically normal and in good general health.

Exclusion criteria

Patients:

• 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.
• Previous head injury.
• Present or past (within past 6 months) drug or alcohol abuse or addiction as determined by a qualified study neurologist/psychiatrist.
• Radiation treatment to the brain during a three-month period prior to the experiment.

Healthy volunteers:

• Any neurological or psychiatric disorder (e.g., epilepsy, schizophrenia, etc.)
• Previous head injury.
• 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.

ADDITIONAL EXCLUSION CRITERIA FOR MRI SCAN:

Patients and Healthy volunteers:

• Women who are pregnant and women of child-bearing potential who refuse to undergo a urine pregnancy test will be excluded from fMRI experiments.
• Subjects who have contraindications to MRI scanning will be excluded from fMRI experiments but included in cognitive experiments. These contraindications include:

• central nervous system aneurysm clips;
• implanted neural stimulator;
• implanted cardiac pacemaker or defibrillator;
• cochlear implant;
• ocular foreign body (e.g., metal shavings);
• insulin pump;
• metal shrapnel or bullet;
• any implanted device that is incompatible with MRI.
• 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.