Attention: the most common cognitive disturbance in neurocognitive patients involves the domain of attention. It is the capacity of harnessing one’s own neural resources on the processing of one item of information while excluding all others. Attention is comprised of 5 general categories (Fuster, 2009):
- Alert State (alertness): People’s level of consciousness, or general wakefulness, is defined as how quickly and appropriately people respond to stimuli. The person with prefrontal damage or dysregulation is generally less alert than someone without such damage, especially when the damage or dysregulation is widespread. Generally, the less alert individual is also compromised in spontaneity and general awareness of environmental events than normal.
- Set: Set is the ability to devote enough neural resources for what will happen, or expected events. It is the prediction based on current context of “now.” Set depends on long-term memory, recent memory, perception and the ability to adjust one’s actions based on the match or mismatch of the expectation.
- Spatial attention: The basic ability to gauge the spatial orientation of one’s own body in the environment. In a brain-injured patient (or a patient with prefrontal dysregulation), spatial neglect (impaired spatial attention) is a more specific type of spatial attention whereby the patient lacks full awareness of his or her body. It often presents on one side only. Spatial attention allows the person to be able to adjust actions based on their own predictions of environmental changes. When impaired, it produces an inability to anticipate and correct for changes in the world around the person.
- Sustained attention: The ability to maintain concentration. Patients with prefrontal damage or dysregulation reach their limit quickly in sustaining their own attention. The more complex the activity, the more the attention is taxed quickly and the more the deficits are evident. Since working memory is a form of sustained attention, people with prefrontal lesions or dysregulation are almost uniformly deficient in working memory.
- Interference control (resistance to distraction): This is what it sounds like. The person with prefrontal lesions or dysregulation will demonstrate deficits in resisting environmental events interfering with tasks at hand. This person would be unable to resist paying attention to irrelevant information, including information from their own body states.
Attention-Deficit Hyperactivity Disorder: (ADHD) is an incurable, pervasive neurological disorder present in all parts of the world and cultures. It affects between 7 and 12 percent of children, and is reported to be slightly less in adults. Treatments involve medications, behavior and cognitive therapy, and family therapy.
Brain network terms:
- Node: principle network unit and linked (connected) to other nodes (also called vertices).
- Network: consists of a number of given nodes connected together.
- Edge: a link or communication pathway between two nodes in the network. Axons are the links between neurons.
- Degree: the number of nearest neighbors to which a node is connected.
- Mean degree: the mean of the individual degrees of all the nodes in the network.
- Modules: clusters of neurons with high density of nearest neighbors and high degree nodes (local communication).
- Hubs: regions that link distinct clusters or modules with high functional connectivity density.
- Provincial hubs: hub regions which are highly connected within one module.
- Connector hubs: hub regions that link multiple modules.
- Scale-free network—distribution of node number follows a power law.
- Topology: specific pattern of links or connections which defines the network.
Brodmann Areas: defined in 1909, by Korbinian Brodmann based upon differences in the cytoarchitectural organization of neurons he observed in the cerebral cortex. These areas were later validated in the 1990s with the advent of new imaging technologies such as fMRI and PET. There are 88 Brodmann areas forming the basis for our understanding of brain function and a major contribution in neuroscience.
Executive Functioning: the principal function of the cortex, it is the ability to temporally organize purposive behavior, language and reasoning toward a goal.
Imaging modalities: In the past several decades, there have numerous imaging techniques developed for measuring all aspects of brain structure and function. Each technique has certain advantages as well as limitations.
- CT scan (computed tomography) is a computerized x-ray that takes multiple pictures then produces a detailed image from them. It is used to identify abnormalities in the brain and body.
- MRI (magnetic resonance imaging) is a widely-used technique for obtaining static high resolution images of the body using powerful superconducting magnets and radio signals. Images can be weighted with more or less magnetization depending on the nature of the anatomy being examined for structural integrity or pathology. T1-weighted images are typically used for examining the cerebral cortex, whereas T2-weighted images are better for examining white matter lesions.
- BOLD fMRI (blood oxygen level dependent functional magnetic resonance imaging) a functional imaging process which builds on MRI to map BOLD hemodynamic responses, an indirect measurement of neuronal activity.
- DTI (diffusion tensor imaging) is an MRI platform that can produce a “wiring diagram” of the brain, examining at the integrity of the brain’s neural pathways (white matter fibers) in order to detect various brain pathologies. Although DTI is relatively new it has proven to be an invaluable research tool paving the way for major advancements in neuroscience. Clinical usefulness for DTI remains to be established.
- PET (positron emission tomography) uses a radioactive isotope emissions to measure physiological function by looking at blood flow, glucose metabolism, neurotransmitter activity, and radioactive drugs.
- SPECT (single photon emission computed tomography) is similar to PET and relies on a radioactive tracer to measure cerebral blood flow.
- LORETA (low resolution brain electromagnetic tomography) is an electrical neuroimaging method that takes the EEG signal at the scalp surface and computes the current sources that gives rise to that signal. Brain maps generated reveal a 3-dimensional distribution of sources throughout the brain at spatial resolution within 1 cm. LORETA also uses the same coordinate system as fMRI, PET, and SPECT to allow direct comparison of findings.
Memory: It is difficult to define memory without understanding brain networks. Brain networks (connectomes) are widely distributed throughout the cortex, associating different clusters of neural assemblies. Memory systems are known as representations, since they contain not only the verbal and visual knowledge as part of the memory, but also the goal-directed action sequences . In this manner, these networks represent past, and future actions.
People with prefrontal cortical lesions or dysregulation are normally not markedly amnesic, but they do have trouble with recall and recognition with their primary deficit being in organization and monitoring of verbal material. Recent memory is also impaired due to their issues with perceptual attention and drive. Paradoxically, they have very little difficulty on neuropsychological tests of declarative or episodic memory.
- Working memory is the ability to keep relevant information “in mind” when performing a task. It is a combination of the essential cognitive functions of speech, reasoning and goal-directed prospective behavior. Working memory is a necessary condition for prospective action, regardless of whether the to-be-performed action is motor, speech or a mental operation. Working memory problems are consistently seen in persons with lateral prefrontal damage/dysregulation; it appears to be distributed throughout the lateral prefrontal cortex, and due to its characterization as sustained attention to internal stimuli, it is subject to interference and distractability. People with cortical damage may still perform well on some working memory tests. Accurate testing requires a test that introduces interference and distraction.
Neurocognitive Disorder (NCD): This “umbrella” term was introduced in the Diagnostic and Statistical Manual of Mental Disorders, 5th Edition (DSM-5, American Psychiatric Association, 2013). Nearly all major NCDs include the dementias (e.g., Alzheimer’s disease, vascular dementia) with specifiers of mild, moderate, and severe. Major NCDs are to be distinguished from mild NCDs (e.g. mild NCD due to Parkinson’s or some other medical condition), cognitive disturbance that does not meet criteria for dementia. There are six different cognitive domains affected by NCDs described in DSM-5: complex attention, executive function, learning and memory, language, perceptual motor, and social cognition.
Planning: Planning is foresight, or “memory for the future.” Failures in plan formation are the opposite of deficits in working memory, in that difficulties in planning involve prospective thinking. Working memory is about the past and to some degree, the present while planning involves the future. Like working memory, planning is vulnerable to problems with distraction and attention. Planning deficits tend to occur alongside working memory problems, as a function of lateral prefrontal cortical dysregulation.