Cognitive Neuroscience: A Very Short Introduction

A Recent Field

• Visualization Techniques:
  • PET (Positron Emission Tomography) - 1980s
  • fMRI (Functional Magnetic Brain Imaging) - 1990s - the ratio of oxygenated to de-oxygenated blood.
• Help us learn about:
  • Human capacities
  • Human limitations
  • Disorders of the nervous system

Perceiving

• Lateral Occipital (LO) complex - an area that is activated when people recognize objects. Critical for the ability to use the ahape and orientation of an object to guide the way in which the hand approaches it.
• Information from vision, hearing, touch, and smell is relayed to from the sense organs to separate regions of the brain, which are referred to collectively as the primary sensory areas:
  • V1 - the primary visual area, with secondary areas V2, V3, V4, etc. The primary visual cortex relays information via these and other areas to the temporal lobe and the parietal lobe. These relays are termed the ventral and dorsal visual pathways.
• The brain has a parallel architecture with some choke points
• Localization of function - the brain is a patchwork of discrete areas. Each area consists of a host of neurons arranged in six layers, each layer being many neurons thick. The areas differ in the thickness of the layers, the density of the packing, and the frequency of the different types of neuron.
• The incoming connections determine the information that the area can process, the outgoing connections determine the influence that it can exert on other areas.
• The outside world is mapped onto the brain in a point-to-point fashion. The primary somatosensory area (S1) is a map of the body with different parts responding when the hands, body, or legs are touched. In the primary visual cortex (V1) there is a retinotopic map - the retina is mapped onto the cortex such that the location of the activity in the cortex depends on which part of the retina is stimulated by light.
• Because we use our hands for manipulating objects, much more tissue is devoted to the hand than to the foot. In the V1, more tissue is devoted to central than peripheral vision. In the centre of the eye there is a pit or fovea and it is here that there is the greatest density of light receptors. When we inspect an object is is with the fovea that we focus our gaze.
• Integration between sensory modalities is achieved by connections to common reas, and these are referred to as "multimodal" areas, including the parietal cortex and the prefrontal cortex. These areas are multimodal because they can be activated irrespective of whether the stimuli are visual, auditory, or tactile.
• Processing occurs via successive stages in the visual relay. The earlier stages process the elements and the later stages integrate them via a hierarchical arrangement in which each higher-order neuron in area B receives an input from many lower order neurons in area A, and so on up through the stages.
• Lower-order neurons respond maximally when we see an object from a particular view whereas higher-order neurons integtrate the information from lower order neurons and are thus able to learn to respond irrespective of the view to let us form a view-independent representation of the object.
• As a child we are taught that different animals are primates or birds. The suggestion is that the representation of these categories is learned by groups of neurons in higher areas through the association of inputs from lower-order areas.

Attending

• At any time you are only interested in some of the information that is available. This is particularly true for what we see.
• Activation is greater when attending than when not doing so in two regions - the intrapiarietal sulcus and the frontal eye field (the dorsal attention system). Both areas are also engaged when people actually move their eyes or simply plan to move their eyes. When you attend to the periphery while gazing centrally, the enhanced activation reflects the fact that you are preparing to move your eyes.
• No behavioral process depends on a single area of the brain - activations are distributed across the brain. So anatomical systems support functional systems.
• An object catches our attention either because it is salient or because we are looking at it. In either case, if the object is in peripheral vision we move our eyes so as to bring it into central vision.
• In spatial neglect, eye movements are almost entirely confined to the right hand side of the display. Neglect most often results from strokes that involve the right parietal cortex. In a stroke the blood supply to an area is cut off, either because of a blockage or leakage in an artery. The effect is that the neurons in the area that is supplied by that artery die through lack of oxygen and glucose.
• The inferior parietal cortex and the temporo-parietal junction (TPJ) form part of the ventral attention system. The TPJ forms a critical node at which the temporal and parietal cortex can interact.
• Target detection tasks provide one situation where that interaction is required. The ventral visual stream is involved because the letters are identified on the basis of their shape; and the parietal cortex is involved because some of the targets will appear in peripheral vision.
• If a large stroke affects the left parietal cortex, the right inferior parietal cortex and TPJ are still available for detecting targets whether they appear on the left or the right. But after a large parietal lesion on the right, the left parietal cortex can only support detection of targets on the right.
• Mental distraction led to a decrease in the activation in the sensory pathway in the spinal cord, and the people also reported that they felt less pain. The signals that cause this reduction originate in the prefrontal cortex. It sends top-down signals that appear to evoke a release of opiates in the system and it is this release that moderates the pain.
• The fusiform face area (FFA) is involved in the discrimination of faces.
• Top-down signals can:
  • Set up a task by enhancing processing in the relevant sensory stream.
  • Set up the targets by creating a template against which they can be matched.
  • Inhibit processing in irrelevant input streams.
• The ventral prefrontal cortex transforms sensory input into motor output. If it is to transform any input into any output it needs a matrix of interconnecting neurons so that routing through the area allows for maximum flexibility.

Remembering

• Unlike small objects, which we can fixate in central vision, scenes are extended and so they fill our visual field. The parahippocampal cortex is activated if people are scanned while they view pictures of scenes or large objects such as houses that could serve as landmarks
• The hippocampus represents where we are, and people with damage to it have trouble finding their way around.
• Why does an animal want to remember a place? Because that is where they saw food, a mate, or their offspring. But the world changes, so it pays animals to know not only where they last saw these things, but also when.
• During recall, the hippocampus, retrosplenial cortex, posterior cingulate cortex, and the medial and inferior parietal cortex are activated to provide a feeling of reinstatement or the subjective feeling of reexperiencing the event
• The hippocampus provides the spatial context for events, whether the context is actually present or only there in the imagination. The events are autobiographical or personal because we were present at the time. And recall depends on the process of reinstatement in the cortex. It is this that we experience as reliving the event.
• In the case of semantic knowledge there is activation in the middle and inferior temporal cortex extending to the perirhinal cortex, which lies at the temporal pole. There is also activation in the ventral prefrontal cortex with which these are connected. The activations in common for pictorial and verbal questions are all in the left hemisphere, which is specialized for language.
• There is a clear distinction between a medial system for remembering events in our life, and a ventral and lateral system for knowledge concerning objects. The perirhinal cortex is concerned with object-specific semantic information and it is increasingly engage as the number of semantic features that objects share increases. Damage to it can lead to problems in naming things and the problems become worse, the more they are perceptually and semantically confusable.
• Remembering personal names is one of the most taxing semantic tasks and is particularly sensitive to ageing. Seven years before there is a severe memory problem with alzheimers, it is possible to detect a loss of colume in the hippocampus.