Greg Detre
Wednesday, 24 May, 2000
Prof. Rolls - B&B IV
The frontal lobe has long been ascribed higher, intellectual or executive functions � this tradition can be traced back to the well-known case of Phineas Gage (from Damasio, 1994). After miraculously surviving an iron rod passing straight through his skull, Gage was transformed as a person. The rod caused most damage to his left frontal lobe, and left the formerly religious, friendly and competent foreman unable to hold down a job, disreputable and prone to inappropriate swearing and social behaviour.
The frontal lobe includes all the tissue in front of the central sulcus (approximately 20% of the entire neocortex), and can be divided functionally into three main categories: the motor, premotor and prefrontal.
There are parallel cortical motor systems for movements of the limbs and eyes. There are also two premotor systems, both with a map of the whole body. These play a role in the selection of movements, and differ in their reliance on information about the external context.
The prefrontal cortex as a whole selects actions when the subject must make a new decision as to what to do. It is not yet clear whether prefrontal cortex is only engaged when there is no external cue at the time of the response.
If new decisions are required when a task is learned, prefrontal cortex is activated. But if the task can later be run off automatically, prefrontal cortex need no longer be engaged.
The exact role played by the basal ganglia is not clear. In animals without neocortex, such as amphibians, the basal ganglia form the telencephalic mechanism for determining responses. In mammals, the frontal cortical and basal ganglia are closely interrelated via a system of loops. There are suggestions that the ventral striatum may play a role in the process by which the probability of a response is altered as a result of positive or negative outcomes.
The motor cortex (Brodmann�s area 4)
premotor cortex - lateral area 6
lateral premotor area has expanded as Broca�s area (44) has developed
supplementary motor cortex - medial area 6
frontal eye field � area 8
supplementary eye field - area 8a
curious name � Rose + Woolsey�s observation that it received projections from the dorsomedial nucleus of the thalamus
primates 3 regions:
dorsolateral prefrontal cortex (areas 9, 46)
inferior (or ventral) prefrontal cortex (areas 11, 12, 13, 14)
= orbital frontal cortex (11, 13, 14) because the orbit (socket) of the eye
medial frontal cortex (areas 25, 32)
= sometimes considered part of the anterior cingulate region rather than prefrontal cortex
2 multimodal areas of the frontal lobe = the lateral premotor cortex (area 6) and area 46
The prefrontal cortex is one of the most recently evolved and massively developed areas of the primate, and especially, human brain.
prefrontal lobotomies, pioneered by Moniz (Moniz, 1936; Fulton, 1951) � argued that anxiety, irrational fears and emotional hyperexcitabilty in humans might be treated by damage to the frontal lobes
widespread use of this procedure � although irrational anxiety or emotional outbursts were sometimes controlled � but intellectual deficits and other side effects were often apparent (Rylander, 1948; Valenstein, 1974)
still had pain, but it no longer bothered them (Freeman & Watts, 1950; Melzack & Wall, 1996)
Shallice etc.
As in monkeys, the prefrontal cortex is also crtiically involved in the process by which the human brian generates and selects actions. Human beings can select between ideas, and the prefrontal cortex has been elaborated to allow the selection of mental responses.
Human beings can also plan future actions and select between them by mental trial and error. The consequences of this development are far-reaching, because it means that human beings can set themselves goals other than simply promoting their genes in the next generation. Human beings are capable of �voluntary� action in the most restrictive sense.
Using imaging technology, scientists from the National Institute of Neurological Disorders and Stroke (NINDS) found that a specific type of multitasking behavior, called branching, can be mapped to a certain region of the brain that is especially well developed in humans compared to other primates. The study will appear in the May 13, 1999, issue of the journal Nature.1
"The results of this study suggest that the anterior prefrontal cortex, the area of the brain that is most developed in humans, mediates the ability to depart temporarily from a main task in order to explore alternative tasks before returning to the main task at the departed point," says Jordan Grafman, Ph.D., Chief of the Cognitive Neuroscience Section at the NINDS and a co-author of the study.
The investigators used functional magnetic resonance imaging (fMRI), which measures changes in blood flow to the brain, to view the brains of volunteers while they performed branching tasks. The region of the brain that is involved in multitasking is called the fronto-polar prefrontal cortex (FPPC).
Tasks performed by the volunteers involved exercises to test working memory, attentional focus, and a combination of the two. All of the subjects, who were healthy, normal volunteers, participated in all of the task groups. The task groups consisted of a control task, a delayed-response task, a dual-task, and a branching conditions task. Dual-task involves changing focus between alternative goals successively. The investigators predicted that subject performance on the individual delayed-response task and dual-task conditions would not activate the FPPC. They did predict that the branching task which involves problem solving and planning would stimulate activity in the FPPC. According to the fMRI data, their predictions were correct. The FPPC was activated only during those tasks that involved an interaction between working memory and attentional focus decisions.
The FPPC is the region of the brain that controls complex problem solving and is especially well developed in humans as compared to other primates. The study showed that the FPPC selectively mediates the human ability to multi-task.
does it do one thing? � functional specialisation of different bits of the prefrontal
incl the orbitofrontal � 4 lines (emotion)
humans & monkeys equally