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Neuroscience 3

1.) The Human Amygdala - Whalen & Phelps - Coverage of the amygdala with reference to a wide area of neuroscience

2.) Mind in Life - Evan Thompson - Describes the enactive approach to consciousness

3.) The Root of Thought - Andrew Koob - Emphasises the role of astrocytes in brian function

4.) The Synaptic Self - Joseph Le Doux - Readable account of brain plasticity and memory and of relationship between prefrontal and limbic areas.

1.)

The Human Amygdala

Eds: Paul Whalen & Elizabeth Phelps

This book gives coverage of the amygdala, with regard to a wide spread of neuroscience, medicine and psychology. We summarise those chapters that are more relevant to consciousness. In that we are conscious of emotions, and recent research has led to an increased emphasis on the function of emotion in determining brain processing and behaviour, the best possible understanding of emotions seems relevant to any study of consciousness.

Chapter 1

Neuroanatomy of the Primate Amygdala

Jennifer Freese & David Amaral

The amygdaloid complex is located in the medial temporal lobe just in front of the hippocampal region. Studies in recent decades show that the amygdala has a network of connections, both inward and outward, with many parts of the brain, beyond its traditionally recognised connections with the hypothalamus and the brain stem. Its nuclei can influence diverse regions including the spinal cord, frontal, cingulate, temporal and occipital cortices. Projections to the amygdala from the frontal lobes come mainly from the orbitofrontal and parts of the media prefrontal. These areas are related to social activity. The amygdala has substantial connections with the temporal lobe, and reciprocal connections with a variety of subcortical regions. The lateral nucleus of the amygdala, occupies a larger proportion of the total amygdala in primates including human than in other mammals. This is related to this nucleus receiving many inputs from the neocortex. The upper parts of the lateral nucleus receive inputs from the sensory cortex. The primate amygdala is involved with all types of sensory information, but is most heavily influenced by the visual. The largest proportion of visual input comes from the ventral 'What?' pathway indicating that the amygdala is to a good extent a danger detector that can orchestrate a whole body response.

Chapter 2

The Human Amygdala: Insights from Other Animals

Joseph LeDoux & Daniella Schiller

The word amygdala denotes an almond shaped structure in the medial temporal lobe, although the almond shaped area is now recognised as a sub-division of the full amygdala. The evolutionary newer part of the amygdala is associated with the cortex. Output connections from the central amygdala to the brainstem are involved in controlling emotional reactions, while outputs from the basal amygdala to the striatum are involved in controlling physical actions. Most of the inputs to the amygdala involve excitatory pathways that use glutamate as a neurotransmitter. The amygdala is subject to three categories of neuromodulators. Peptides are released locally from axons within the amygdala; amine transmitters are transmitted from distant parts of the brain; hormones reach the amygdala via the bloodstream. The amines, noradrenalin, dopamine serotonin and acetylcholine are released in the amygdala and influence how excitatory and inhibitory neurons interact. Output connections of the amygdala's central nucleus terminate on modulatory networks in the brainstem. Activation of the amygdala leads to the release of modulatory chemicals throughout the forebrain. The various neuromodulators have more diffuse effects than excitatory and inhibitory transmitters, which mostly act at specific synapses. The positioning of receptors in the amygdala determines which areas respond to which neuromodulators. Damage to the amygdala produces changes in fear reactivity, feeding and sexual behaviour. The amygdala is also implicated in reward learning, motivation and drug addiction. It has been implicated in aggressive, maternal, sexual and eating/drinking behaviour. It is also involved in the modulation of various cognitive functions such as attention, perception and memory.

The amygdala has extensive connectivity with areas of the brain involved in cognitive functions. Once the amygdala has detected an emotional stimulus, it can also influence the processing of that stimulus. The amygdala also projects to association areas in the temporal lobe. Cognitive functions are able to influence the amygdala, and prefrontal executive areas have some influence. Cognitive activity such as reappraisal can alter activity in the amygdala. The amygdala can also influence cortical functions indirectly. When the amygdala detects something emotionally significant, it directs the release of neuromodulators, such as noradrenaline, dopamine and serotonin that influence cognitive processing in cortical areas. Amygdala activity also releases hormones into the bloodstream that later feed back from the body to the brain. Activity in the basal amygdala influences hippocampal processing of memory.

Chapter 4

Amygdala Function in Positive Reinforcement

Elizabeth Murray, Alicia Izquierdo & Ludise Malkova

The amygdala can link neutral sensory cues such a light or sound signals with an aversive experience such as an electrical shock. The amygdala is also involved in positive reinforcement. The authors view the amygdala as endowing cognitive constructs, such as words, rules and concepts with emotional valence. This works partly by linking neutral representations with innate response mechanisms. The amygdala is essential for associations that are needed for survival, such as food seeking, reproductive, parental and defensive behaviours. The amygdala appears to link sensory inputs with autonomic reflexes. It can assign positive or negative values to neural representations of sensory inputs. The authors point to the connection between the orbitofrontal and the amygdala, concerning the relative value of objects and actions stored in the orbitofrontal. This accounts for the emotionally laden nature of particular words or images. One function of the amygdala is to assign value to object representations, and this could also extend to abstract concepts. Damage to the amygdala can lead to deficits in recognising fear or trustworthiness. Amygdala based values may guide social interactions. The preference for particular objects can be unconsciously acquired via the amygdala. Patients with amygdala damage do not acquire preferences in this way.

Chapter 8

The Human Amygdala and Memory

Stephan Hamann

Research points to emotion as being important in influencing the strength and subjective quality of memories. The emotional quality of memories is seen as adaptive, because positive or aversive memories of events have more influence on behaviour than neutral memories. The evidence suggests that emotionally arousing events are better remembered than neutral events. The brain mechanism involved is the amygdala located within the temporal lobe and close to the hippocampus. There are plentiful connections between the amygdala and the hippocampus. The amygdala is seen as facilitating the encoding of emotional memories in other parts of the brain, rather than storing the memories itself. In emotional events, the attention is regarded as narrowing or focusing on the central emotional issues. Emotional arousal involves increased activity in the amygdala, leading to increased activity in the medial temporal lobe, including the hippocampus, entorhinal cortex and related structures. Emotional arousal has been demonstrated to increase synchrony between neuronal firing in the amygdala and the hippocampus at the theta frequency.

New episodic memories are thought to undergo a process of consolidation that converts them into a more permanent form. Hormonal influences, for instance those related to stress can play a role in the consolidation process. The author claims that there is growing evidence for consolidation of emotional memories taking place during sleep, particularly REM sleep. (Holland & Lewis, 2007: Wagner et al, 2006). Cognitive processes, such as thinking about an event, can also reinforce emotional memories. The hippocampus is seen as having a special role in the recollection of memories, although they are stored more generally throughout much of the cortex. Activity in the ventral striatum, a brain region involved in reward, is correlated with memories of positive stimuli. Many of the same structures that are involved during emotional memory coding are also involved in retrieval, but in this case they seemed to be more involved with the subjective experience than the historical accuracy of the memories. The amygdala's interaction with both the medial temporal lobe regions and the prefrontal cortex is enhanced during the retrieval of emotional memories. Retrieval of emotional memories involves enhanced bidirectional activity between the amygdala and the hippocampus. The amygdala facilitates access to earlier subjective or emotional states, and preserves current emotional states for future access. It is also involved in the imagining of possible future emotional events. For non-declaritive or non-conscious memories traces are stored in the amygdala, but for declarative or conscious memories of incidents or facts the amygdala only modulates the activity of the hippocampus and related structures.

Chapter 10

The Role of the Human Amygdala in Perception and Attention

Patrick Vuilleumier

The amygdala is associated with the motivational value of environmental events. The amygdala projects to many output systems such as the autonomic, motor, memory and cognitive systems. It is said to resemble a Grand Central Station of the brain. Emotions are here seen as the appraisal of and response to events. The amygdala is positioned to modulate cortical pathways involved in perception and attention, which may in turn affect memory and cognitive functions. This can lead to an influence on goal directed behaviour. Attention is seen as a selection mechanism for deciding what to respond to in the environment. Unattended events do not usually enter consciousness. Emotion appears to have a parallel selection process in deciding what should be processed. The authors states that there is evidence that attention is directed towards emotionally significant stimuli. This is regarded as having evolutionary advantages. Attention and emotion are therefore not entirely separate systems, although some of the mechanisms involved may be distinct.

Visual scenes with emotional content are shown to produce greater activation in the occipital cortex than neutral scenes. The same applies to the auditory cortex relative to sounds. Studies show increased activation correlated with amygdala responses. The amygdala is not just responsive to fear cues, but also to positive cues and to ambiguous cues. Emotional as opposed to neutral targets are more quickly picked out from among distracters. This is related to the amygdala function. The amygdala projects to widespread regions in the cortex, including all stages of the perceptual pathways.

The basal forebrain receives dense inputs from the amygdala, and in turn projects to the frontal, parietal and sensory cortices, where neural responses can be amplified or sustained. Interactions between attention and emotion may involve projections from the amygdala to the orbitofrontal and cingulate cortices.

Emotional signals from the amygdala to the cortices may act in parallel to other top-down signals to the cortices, particularly those due to voluntary attention that are under frontal and parietal control. Emotional information may be monitored, even when it is outside the current focus of attention. This is supported by a number of studies. Attention and emotion are here regarded as interactive. Emotional influences are seen to arise outside voluntary control and awareness, but may be either amplified or reduced in the amygdala that may in turn be influenced by inputs from the orbitofrontal. On the other hand, activity in the orbitofrontal and cingulate may be increased, when emotional cues have to be overridden. Emotional modulation may also produce lasting changes in perceptual pathways. Thus emotional processing may not just appraise sensory inputs, but may regulate perceptions and organise attention.

2.)

Mind in Life

Evan Thompson

Harvard University Press

INTRODUCTION: Embodied dynamism or the enactive approach developed out of the apparent short comings of late 20^th century cognitive science. The central idea is that mind is embedded in the body, the motor actions and the external environment. Autonomy is seen as a key feature of living organisms, and the world of the cognitive being emerged from the interaction of body, brain and environment, with consciousness linked to this and seen as a central feature, rather than a by-product as in more traditional cognitive science. This book calls for an expanded notion of the physical to account for the subjective element within the physical world. However, although the approach may appear more flexible and thoughtful than more traditional cognitive science, in the end there remains an explanatory gap as to why the inclusion of the body and the environment gives rise to a consciousness that cannot be found in the brain as described by neuroscience.

The term cognitive science arose in the late 20^th century, as research that embraced neuroscience, psychology, linguistics, computer science and artificial intelligence. The goal was to make explicit the mechanisms of cognition. Cognitive science began as part of a revolution against behaviourism, which had dominated thinking in these areas through much of the 20^th century. Behaviourism thought in terms of sensory input and prior conditioning. More recently, cognitive science has been criticised for neglecting emotion and subjective experience.

Three approaches emerged in cognitive science, the mind as computer, the mind as neural network (connectionism) and embodied dynamism (enactive approach). Classical cognitive science was based on the computer model of the brain, which required internal processing. Both brain and computer are viewed as symbol-manipulating systems. Non-symbolic sensory inputs to the brain are transduced into symbolic representations. These symbols are manipulated in a formal way to produce the solution to a particular problem. The focus is on abstract problem solving, the content of symbolic representations and the nature of the algorithm for solving the manipulations. This form of cognitive science was linked to functionalism, which claimed that only the abstract system mattered for generating mind matter, and it was irrelevant whether it was embodied in a brain, a silicon computer or some other system. Cognitive science is seen as inheriting a taboo on discussing consciousness from behaviourism. The inner symbol language of the cognitive science brain was viewed as non-conscious. Consciousness was seen as merely having access to the results of non-conscious processing. This processing is in a kind of CPU separate from consciousness, emotion, perception and motor action. Cognitivism made no attempt to provide an account of subjective experience. Connectionism provided a limited critique of cognitive science. It focused on the limitation of the symbol system in terms of non-conscious processing. Connectionist models of cognitive processing take the form of artificial neural networks. There was an emphasis on pattern recognition, rather than deductive reasoning.

Embodied dynamism or the enactive approach that emerged in the 1990s included the implications of the mind being embedded in the body, motor actions and emotions and the external environment. It is still accepted in this approach that most processing is unconscious. However, the followers of the embodied dynamic approach had, in some cases, a greater wish to form a link with subjectivity. Varela, Thompson and Rosch developed this approach in the early 90s. They emphasised that living organisms were autonomous. Nervous systems were also seen as autonomous, because they maintained their own levels of activity. Cognition was viewed as emerging from patterns of perception and action. The world of a cognitive being is argued to arise from interaction with the environment, rather than being a pre-specified activity. Consciousness was something central, rather than an unimportant by-product. Consciousness and the autonomy and intentionality of living entities were seen as being linked. According to the enactive approach, mind emerges from the interconnected brain, body and environment. The autonomy of living entities is emphasised, as opposed to behaviour being determined by input/processing/output.

Phenomenology as derived from the philosopher, Husserl, emphasised that we can adopt differing first-person stances towards the world. It is possible to step back, and examine the actual experiences that we are having. The concept of reality is seen as involving the activity of consciousness. The self is viewed as formed by its individual history, the body, the environment, and as being something concrete with convictions, interests etc., as a result of accumulated experience.

In recent years, there has been interest in a dynamical approach to cognition and emotion. Biological processes are often non-linear. This leads to complexity or chaos that is neither random nor predictably ordered. This presents a very different picture from the idea of the brain as a digital computer. Also, in contrast to computer models, dynamical systems are seen as evolving in real time. The autonomy that is stressed to be an important feature of living entities is defined as the capacity to manage a flow of energy through the organism, so as to manage its own internal processes. In the nervous system sensory activity and movement are thought of as coupled in a continuous circular fashion. Meaning is seen as the result of the brain system coupling with the environment. Something acquires meaning for an organism to the extent that it relates to maintaining the organism's integrity. The system needs a semi-permeable boundary, such as a membrane and an energy currency, such adenosine triphosphate (ATP), which transfers energy from the breaking of chemical bonds to energy-absorbing reactions within the cell. A cell stands out as a unit that has an external boundary, and can regulate its interactions with the environment.

Cognition, emotion and action require the integration of widely distributed brain regions. An important question for modern neuroscience is to determine the method of this integration. Some theorists see instability or metastability as important, in order to prevent the system being trapped in a single state. In the theory of autopoiesis formulated in the 1970s, Maturan and Varela focus on the living cell. A cell is a thermodynamically open system continually exchanging matter and energy with the environment. The cell produces its own components, which in turn regenerates the cell. There is a self-perpetuating loop of reactions. This circular process is known as autopoiesis. The cell membrane serves as a barrier to diffusion between the cell and the environment, but permits the exchange of specific matter and energy. The cell is sustained by a network of chemical transformations that would be drowned out without the protection of the membrane. The membrane itself is also produced and maintained by the chemical network that it protects.

The author discusses the relationship between autopoiesis and cognition. An organism has to aim beyond itself, and thus to have a type of self, in order to exchange matter and energy with the environment. The self emerges along with a domain of interaction with the environment. This is seen as being linked to subjective consciousness. Autonomy is the basis of agency and meaning. Intentionality is taken as being a form of self-organisation. The organism is viewed as an integrated whole rather than something that is atomised, and its development is seen as interactive with the environment.

Animal life is viewed as distinct from plants and fungi, in requiring sensorimotor activity, in order to obtain nourishment. Sensorimotor activity involves movement, perception and finally emotions. Feeling the presence of one's own body is seen as the beginning of consciousness, but also implies a feeling for the self and the environment. It is claimed that the separation of life and consciousness in neuroscience has made it impossible to understand consciousness. Physical accounts have tended to characterise the human system from the outside, while consciousness is described from the inside, thus leaving an explanatory gap.

If mental processes are bodily processes, then there is something it is like to have bodily processes. What is required is an expanded notion of the physical to allow for the subjective aspect of the physical. This in particular needs to take account of the autonomous nature of organisms and their lack of thermodynamic equilibrium. In physics appearances can be reduced to underlying causes that exclude the subjective experience, but with consciousness, the subjective appearance is what constitutes consciousness.

The author argues that the human mind is embodied in both the body and the environment around it. Mental life involves three over lapping types of activity, self-regulation, sensorimotor coupling with the environment and subjective activity. The subjective part is cognition, plus the emotionally charged interaction with the self and the surrounding environment. The understanding of consciousness is here linked not to intrinsic neural activity by itself, but interlinked with the body and the environment. Things are perceived in relation to our moving bodies. The body manifests itself in perceptual experience and as the self of motor activity. The body is experienced as both subject and object. Bodily consciousness is seen as the convergence of perception and action. The subjective character of experience includes both experience of the external environment and of the body, and also the mental experience of remembering, imagining etc.

Emotion is seen as a whole-brain or even a whole-organism event recruiting and retaining the activity of many brain regions. Emotion involves the brain stem, limbic areas, cortex and visceral and motor areas, nervous, immune and endocrine systems. Emotion is not a reflex, but can be directed towards some future state. Emotion is considered to be essential to all intentional behaviour. There is a large overlap between the cognitive and emotional neural systems.

The author refers to Husserl's view of the present moment, which is not seen as an instantaneous now, but as something having temporal width. It is viewed as a temporal expanse containing past and future phases, a bow and a stern, a forward and a rearward looking part. Husserl viewed the process as first impression, then holding onto that impression, and a final phase that is forward-looking towards the immediate future. Cognition requires the coordination of many separated brain regions, and consciousness is widely thought to be associated with widespread neural activity, rather than any specific brain area.

Consciousness is now often associated with transient synchronous activity in neuron assemblies. The timescale of this activity is suggested to be in the range of 250-500 ms. Specific changes in synchrony are seen to occur in relation to, arousal attention, perception or the operation of working memory. Gamma frequencies are particularly associated with this process, and have been shown to play a role in perception and attention. A neural assembly requires a relaxation time, a period in which it arises, stabilises, and then switches to a new neuron assembly. This relaxation time is seen as comprising a window or temporal frame, within which everything is regarded as the present moment. A study of (Rodriguez, 1999) is as supporting this concept.

3.)

The Root of Thought

Andrew Koob

FT Science Press

INTRODUCTION: This book draws attention to the importance of glial cells and particularly astrocytes in the functioning of the brain. This is an attempt to reverse more than a century of research neglect, since Cajal asserted the overriding primacy of the neuron in brain function. The material here has no immediate connection to consciousness studies, except to remind us that many approaches to consciousness work with an over simplified and unenquiring model of brain function.

The relative neglect of the glia goes back more than a century to Cajal's promotion of the idea that these cells were just a form of buffering between neurons. This idea became entrenched, before it came to be realised that glia were also capable of electrical signaling. Glial cells include Schwann cells, epthelial cells, oligodendricytes, microglia, astrocytes, Moller cells and ependymal cells. Schwann cells are responsible for the mylenisation of axons that allow the rapid transmission of electrical signals. The Schwann cells release the fatty myelin from their cell body, and can swirl it around a group of axons. Oligodendrocytes can also perform this function. Ependymal cells, endothelial cells, tancytes and microglia are involved with the blood brain barrier or other protective functions.

Neurons are seen to be physically dependent on astrocytes, rather than the other way round. Neurons in a petri dish die without astrocytes, but astrocytes can survive by themselves. The presence of astrocytes is also necessary for the formation of new synapses. In the hippocampus, which is involved in the formation of memories, about 80% of large synaptic contacts are surrounded by astrocytes.

The glial cell that has attracted most attention in recent years is the astrocyte. This is the most abundant type of cell in the human cortex. The proportion of glial cells in the brain rises in relation to the intelligence of an animal, and the proportion of astrocytes in the cortex is also greater in more intelligent animals. Synaptic strengthening is seen as the most likely basis of learning, and it is suggested that astrocytes are involved in this process. The author also suggests that astrocytes might be involved in the processing of sensory inputs, and be capable of influencing motor action. Astrocytes are linked to blood vessels, and appear to control the oxygenation of neurons that is required to pump ion channels. Astrocytes also produce proteins in some areas of the brain, and through this can influence the release of hormones into the bloodstream.

Glial cells have been discovered to have a role in the brain's information system. The glial communicate amongst themselves by means of electrical waves triggered by the influx of calcium ions. The glia also receive signals from and send signals to neurons. Neurotransmitters from neurons stimulate astrocytes, and cause an influx of calcium ions. Astrocytes have receptors for every type of neurotransmitter produced by neurons, and these can set off calcium signaling waves within astrocytes. Further to this, it has now been demonstrated that these waves can influence the firing of neurons. A recent study shows that glutamate that was previously thought to be only involved with neurons can also be released from astrocytes, and can cause signaling in neurons. Further, the neurotransmitters, glutamate, aspartamate and GABA cause changes in the electrical potential of astrocytes. Glutamate released from neurons can set of a wave of calcium in astrocytes. Working in the other direction, glutamate released by astrocytes might be taken from the extracellular space by neurons. Astrocyte receptors correspond to the type of neuron that they are near. An astrocyte in the cortex will have glutamate receptors, while an astrocyte in the basal ganglia will have dopamine receptors. Neurons require extracellular calcium to set off synaptic signaling, and some of this extracellular calcium may derive from neighbouring astrocytes.

Calcium ions are seen as crucial to the signaling systems of glial cells. In astrocytes, signaling derives from internal calcium stores. The astrocytes store calcium in three organelles, the endoplasmic reticulum, the Golgi complex and mitochondria. Astrocyte signaling is based on calcium released from storage in the endoplasmic reticulum and mitochondria, and then then spreads to other astrocytes through gap junctions. Astrocytes thus form a net work of calcium signaling. The development of a wave of calcium signals is determined by the pattern of previous calcium signaling in the affected astrocytes. Also, a neurotransmitter acting on an astrocyte can set off a calcium wave spreading from one astrocyte to the next.

Astrocytes are known to form gap junctions with one another. The gap junction determines what can pass from cell to cell. A single astrocyte in the cortex will connect with 50 to 100 astrocytes via gap junctions. Oligodendrocytes that are involved in myelinisation also form gap junctions with astrocytes. Gap junctions can also exist between astrocytes and neurons. It is suggested that astrocytes may turn out to be synchronised, when they are active, in the same way that active neurons become synchronised at particular frequencies.

4.)

Synaptic Self

Joseph Le Doux

INTRODUCTION: This book is a good and readable account of a range of brain processes, notably the relationship between the working memory and executive activities of the prefrontal and the regions of the brain involved in emotional processing, the formation of memory and the synaptic plasticity and cell processes that underlie the latter. As is predictable with a neuroscience book of this kind, the attempt to extend the discussion to consciousness is not successful. Consciousness is viewed mainly as a rather circumscribed aspect of the working memory, but there is no attempt to suggest how it might arise, or what function it performs that could not be achieved by unconscious processing.

Le Doux emphasises the plasticity of the brain. If the brain did not have plasticity, it would not be capable of being modified by experience. There are two main receptors for the excitatory neurotransmitter, glutamate, the AMPA receptor involved in normal synaptic transmission, and the NMDA receptor involved in synaptic plasticity The latter allows the cell to record which pre-synaptic sites were active when the post-synaptic site fired. This process is called long-term potentiation (LTP). This comes in two forms, early and late LTP. The former lasts only about an hour, while the latter is concerned with longer term memories. Calcium, referred to as a 'second messenger', in contrast to the 'first messenger' neurotransmitters, flows into the cell from the NMDA receptor to direct internal chemical reactions. These involve enzymes called protein kinases that render other proteins active by adding a phosphate group (phosphorylation). In early LTP, this process works to increase the number of AMPA receptors.

Late or long lasting LTP, however, requires the creation of new proteins. Activation of particular kinases permits them to move inside the cell nucleus, and activate a gene transcription factor that allows the creation of new proteins that are then transferred to the synapse. There is a widespread assumption that LTP is involved in learning as well as memory. Another influence is the action of neurotrophins that diffuse backwards from the post-synaptic to the pre-synaptic site, where they influence the development of new synaptic connections.

The parahippocampal area and the hippocampus together make up what is known as the medial temporal lobe memory system. Output from the sensory areas converges in the parahippocampal, before being transferred to the hippocampus. The parahippocampal integrates material from different modalities, and is described as a convergence zone. Vision, sound etc. are here put together into a global memory. More abstract concepts can also be formed in convergence zones. Convergence zones are few, except in the brains of primates, and they may be viewed as a marker of cognitive development in a species. The hippocampus is needed for initial memory storage, but over time, the longer term storage in the neocortex becomes independent of the hippocampus. Many researchers think that long-term memories are stored in the parts of the cortex where the initial sensory processing occured. Studies also support the hypothesis that consolidation of memories occurs during sleep, with the hippocampus feeding new memories to the cortex.

There appears to be a link between the activity of the hippocampus and consciousness. Amnesiac patients with damage to the hippocampus can be conditioned to make a response, for instance to a tone that has previously been paired to a puff of air to the eye, but at the same time, they have no conscious memory of the conditioning process itself. There is an apparent distinction between the processing of conscious memories and of unconscious conditioning.

On the basis of various studies of brain damaged patients, it has been determined that the frontal lobes are involved with executive functions, such as planning and control of behaviour, as well as with working memory. Le Doux emphasises the importance of working memory, sometimes referred to as short-term memory, which is involved in thinking and problem solving. The working memory, which can also be regarded as a workspace, can hold only a limited amount of material for a limited length of time, but has the important feature of being able to integrate different types of information and sensation. The frontal lobes are also involved with movement. In primates, there is a greater development of the prefrontal, which lies in front of the movement areas. The prefrontal is regarded as another convergence zone receiving inputs from the sensory cortex, such as the separate 'what' (temporal lobe) and 'where' (parietal lobe) pathways for vision and similarly from the auditory pathways, from the long-term memory and from the hippocampus. The prefrontal is responsible for integrating this information. Reciprocal pathways from the prefrontal back to the sensory cortex can focus attention on particular stimuli. The prefrontal is used in decision taking, including planning several steps ahead. This decision taking may have to be based on imperfect information.

The prefrontal is thought to function as a series of interconnected circuits. The lateral prefrontal is particularly involved with working memory. The anterior cingulate is also involved with working memory. These two areas are closely connected, and form part of the frontal lobe connectional area involved in decision taking and movement control. The ventral prefrontal and especially the orbital prefrontal area are also involved with working memory and especially with emotional information. P. In discussing emotion, this is seen as the process by which the brain assesses the value of stimuli. Signals with emotional content may further create involuntary bodily responses, such as changes in heart rate and blood pressure. Le Doux looks at emotion particularly with respect to fear, because it is the best researched emotion. The amygdala, functioning as a fear centre in the brain, can serve to amplify emotions by triggering responses in the body that send hormones back into the brain. The amygdala can also modulate the flow of neuromodulators, such as dopamine, from the brain stem to the working memory area. The amygdala also has a role in modulating the formation of explicit memories, which may be more vivid as a result.

However, the amygdala interacts with the medial prefrontal cortex and notably with the anterior cingulate and orbital cortex, and these areas have some power to regulate the amygdala and its fear reactions. The relationship between these prefrontal areas and the amygdala is reciprocal. Emotional arousal is seen as being important in the coordination of brain states, including decision making, and can also modulate sensory processing.

The orbital region is connected with the anterior cingulate, and receives information from both the amygdala and the hippocampus. Damage to the orbital cortex results in impairment of social responses and decision taking. The anterior cingulate and orbital cortex are closely connected with one another and with the lateral prefrontal, and are involved with processing both sensory inputs and the short-term working memory. The anterior cingulate and orbital cortex thus form a type of junction between emotional, sensory and memory inputs, on the one hand, and the short-term working memory on the other. Patients with damage to the medial and ventral prefrontal areas show impaired decision taking in emotional situations. Correspondingly, damage to the amygdala impairs the ability to judge emotions in faces and voices. The medial prefrontal is suggested to be an interface between the brains cognitive and emotional systems.

In looking at the brain's reward and pleasure system, the release of dopamine is now seen as more important relative to the anticipation of pleasure, rather than the pleasure itself. The focus is instead on an area known as the nuclear accumbens, which is located in front of the amygdala, and receives sensory inputs via the amygdala. The hippocampus has connections both to the amygdala and the accumbens. The anterior cingulate is also connected to the accumbens. The orbital cortex is also stressed to be important in the processing of motivational, or reward and punishment, information. The orbital, the anterior cingulate, the amygdala and the hippocampus all appear to be closely involved in emotional and motivational processing. The anterior cingulate and the orbitofrontal area in particular are viewed by Le Doux as a single system for integrating emotional and cognitive information and relating it to the working memory.

Le Doux discusses the role of synchronous activity in the brain. This activity is suggested to have a double role, firstly, in binding together processes in different modalities, such as vision and sound, in response to an immediate stimulus, and secondly, in altering synapses in cells in two or more modalities, so that they will respond together, if the same stimulus is presented again. It is emphasised that this suggestion is hypothetical rather than evidence based at the moment.