The Cortex (Organisation and Function of)

The cerebral cortex is wrinkled and layered and folded in on itself in order to increase the surface area (the folds are called 'sulci' and the hills 'gyri'). It's organised into layers, not nuclei like the sub-cortex is.

Corpus Callosum

The corpus callosum connects the two cortical hemispheres and allows them to communicate. It consists of approximately 200–250 million contralateral (horizontal) axonal projections, allowing the two cortical hemispheres to effectively function as single unit.
Although there is believed to be some lateralization of function, where each hemisphere plays a greater role in particular aspects of psychological function (e.g. creativity versus mathematical ability) this is controversial and not accepted by all.

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Occipotal, Parietal, Frontal, Temporal Lobes

Introduction

The frontal lobe is bounded from the parietal lobe by the central sulcus, and bounded from the temporal lobe by the lateral cerebral fissure (lateral sulcus or Sylvian fissure or lateral fissure).

The parietal lobe is bounded from the occipital lobe by the parieto-occipital fissure, and bounded from the temporal lobe by the lateral cerebral fissure, from the end of which a line is drawn to the closest point of the parieto-occipital fissure.

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Each lobe deals with a different sense:

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Occipital - Vision

The Occipital Lobe deals with optics and vision.

Temporal - Hearing + Smell

The temporal lobe deals with hearing and smell.

For hearing, the cochlea transduces sound waves into action potentials (showing tonotopic organisation - done by high v low tones), before transmitting them via the thalamus to the primary auditory cortex.

For smell, chemoreceptors in the olfactory bulb (above the nasal cavity) transduce scents into action potentials. These are sent to the olfactory nerve to distribute to the olfactory cortex (lying on the superior temporal gyrus inside the lateral cerebral fissure), which shows chemotopic organisation (molecularly related chemicals are encoded by spatially related cells).

Parietal - Taste + Touch

The parietal lobe deals with taste and touch.

For taste, chemoreceptors on the tongue, mouth, and throat transduce chemicals into action potentials that are sent along to the nucleus of the medulla solitary tract, the thalamus and then the gustatory cortex (in the parietal cortex).

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For touch, the somatosensory cortex receives input via the thalamus from the sensory receptors within the body.

Occipital-Parietal Intersection

The intersection of the occipital lobe and parietal lobe integrates visual information from the occipital lobe with somatosensory and somatomotor information in the sensory-motor strip. This is the so called dorsal visual stream. Damage to this area results in hemispatial neglect on the contralateral (opposite) side of the body.

The Thalamus

The thalamus (composed of the various thalamic nuclei), has two symmetrical halves (one on each hemisphere), each about the size of a walnut. It's the main switchboard between the cortex and the sub-cortical regions, relaying signals from sensory receptors to the cortex, and back to the SoNS and ANS for behaviour/physiology modification.

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Language

We already knew that language was Left lateralized - building on that, we can see that different regions of the brain light up upon different tasks; hearing words activates the auditory cortex, seeing words the visual cortex, and reading words activates the sensory motor interfaces for the lips/tongue/throat (similar to memory-activation tasks, interestingly).

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Aphasia

The study of aphasia has allowed us to pinpoint Broca's and Wernicke's areas; the former is connected to the motor cortex and is crucial for speech production, whilst the latter surrounds the auditory cortex and mediates higher processing of auditory information (semantic meaning)

Frontal Lobe

The frontal lobe is believed to function as a 'central executive', controlling on-task, goal-oriented, and behavioural actions.

It has been described as being involved with the task of asserting an image of oneself and associating an emotional state with projecting that into the future; damage to it results in changed personalities and a lack of empathy, tying in with that consciousness of self.

Frontal Lobotomy

Frontal Lobotomies were a procedure performed heavily for more than two decades (with more than 20,000 being performed in the USA), where connections to and from the pre-frontal cortex were cut. It was thought to be a cure for various psychological diseases, despite the severe side effects (personality change or complete mental retardation).

Reversal Learning

Reversal learning is where participants are given a task where they must learn to make a choice between two objects to gain an overall positive reward (made up of some losses and some wins) (i.e. always pick white even though sometimes it loses, because black loses more), before the object to choose is switched. The participants are then studied to see if they can learn to choose black over white.

Patients with damage to both hemispheres of the orbitofrontal cortex (OFC) continue to choose the first object/stimuli, whereas patients with no damage, or damage to only one hemisphere were able to learn the change.

OFC damage was hence ruled by Hornak et al (2004) to impair the ability to adapt reward learning to new circumstances.