Prefrontal Cortex

Prefrontal cortex  Connections with sensory systems: o Dorsolateral PFC: Brodman areas 8, 9 and 46. o Ventrolateral PFC: Brodman areas 12 and 45. o These regions receive visual, auditory and somatosensory information from the occipital, temporal and parietal cortices. o Many PFC areas receive converging inputs from two or more sensory modalities. o Areas 9, 12, 46 and 45 receive inputs from the rostral superior temporal sulcus, which contains neurones with trimodal responses to external stimulation.  Connections with motor systems: o Dorsolateral PFC: especially Brodman area 46. o May be the primary region by which the PFC exerts control over behaviour. o Area 46 is interconnected with motor areas in the medial frontal lobe, such as the supplementary motor area (SMA), pre-SMA, anterior cingulate cortex, the premotor cortex on the lateral frontal lobe, the cerebellum and superior colliculus. o Area 46 also projects to area 8, which contains the frontal eye fields. This is important for voluntary shifts of gaze. The prefrontal cortex (areas 9, 10 and 46) has strong reciprocal connections to the premotor cortex (area 6). o Provide higher-order control over the primary motor cortex (area 4). Strong reciprocal connections to the striatum (caudate and putamen).    o The basal ganglia are responsible for many automatic motor functions. Also with the limbic system. o Orbitofrontal PFC (areas 10, 11, 13 and 14) more closely associated with medial temporal limbic structures critical for long-term memory and “internal information” such as affect and motivation. Direct and indirect (via thalamus). o Direct and indirect (via the thalamus) connections with the hippocampus and associated neocortex, the amygdala and hypothalamus. o Strong connections with the olfactory and gustatory cortices. Lesion studies  Gross damage to the frontal lobes may not result in death, as subcortical areas are responsible to maintain the homeostatic adjustments required for life.  Penetration injuries to the frontal lobes can be remarkable because the injured person may well be awake and lucid.  Even penetration injuries that extend further than the frontal lobes may not be fatal, as long as they preserve the hypothalamus and brainstem.  If the penetration damages the primary motor or somatosensory cortices, there will be obvious consequences, but injuries limited to the frontal lobes can produce subtle changes.  Studies have shown that lesions to the prefrontal cortex results in dysexecutive syndrome.  Electrical stimulation of the prefrontal cortex has no obvious effect, but damage can result in behavioural changes. Symptoms of frontal damage  Disinhibition: o Patients are often impulsive, quick to anger and are prone to making rude and childish remarks. o The inability to ignore irrelevant stimuli and the actions they trigger has led to patients with damage to the prefrontal cortex being described as stimulus bound. o Without the influence of goal-related signals from the executive functions, the systems always respond reflexively to an input with whatever output is strongly connected to it.  Emotional impairments: o Damage to the prefrontal cortex produces profound alterations in a patient’s mood and emotions. o Patients typically display an emotional shallowness, being indifferent and apathetic both to their own situation and the needs of others. o They are less able to recognise the emotions of others.  Difficulty planning and impaired working memory:  o Impairments in planning might be related to difficulties in evaluating consequences of actions. o Impairments may also be related to the difficulties in holding information in their working memory. Interpret the intended actions of others, and limit ability to exhibit empathy: o Mirror neurones are located in the prefrontal cortex. o Mirror neurones fire during actual as well as observed movements, and are implicated in empathy. o Disorders of empathy (e.g. autism spectrum disorder, callous and unemotional behaviour and psychopathy) are associated with disturbances in activity of the prefrontal cortex.