Happy Holidays :-)

A Merry Christmas and an enjoyable New Years celebration to you all. I'm off on holiday, so will next post in the new year.

Embodiment and the Mind

Taken from the introduction to the seminal work "Descartes' Error", in the following extract, Damasio describes the often unmentioned link between the brain (and the mind) and the body: generally assumed, but rarely stated - although this emphasis on the role of the body in the proceedings is of course more central in embodied cognition, cognitive robotics, and the like.

"Surprising as it may sound, the mind exists in and for an integrated organism; our minds would not be the way they are if it were not for the interplay of body and brain during evolution, during individual development, and at the current moment. The mind had to be first about the body, or it could not have been. On the basis of the ground reference that the body continuously provides, the mind can then be about many other things, real and imaginary.

This idea is anchored in the following statements: (1) the human brain and the rest of the body constitute an indissociable organism, integrated by means of mutually interactive biochemical and neural regulatory circuits (including endocrine, immune, and autonomic neural components); (2) the organism interacts with the environment as an ensemble: the interaction is neither of the body alone nor of the brain alone; (3) the physiological operations that we call mind are derived from the structural and functional ensemble rather than from the brain alone: mental phenomena can be fully understood only in the context of an organism's interacting in an environment. That the environment is, in part, a product of the organism's activity itself, merely underscores the complexity of interactions we must take into account."

The central thesis of the rest of the book is well known: that 'logical' reasoning and decision making does not, indeed cannot, exist without the central role of emotion processes. This directly contradicted the traditional view of emotion clouding the 'cold', logical reasoning processes - a premise also used by 'traditional' AI (i.e. that not based on environmental situatedness, or some other form of grounding).

Antonio Damasio, "Descartes' Error: emotion, reason and the human brain", 1994, New York: Grosset/Putnam

Encephalon #38

The 38th edition of Encephalon was put at Not Exactly Rocket Science on Monday/Tuesday. Another excellent instalment of the brain sciences blog carnival, with the following contributions being (for me) particularly interesting:

- Firstly, two posts on Mirror Neurons, and how they're not all they're cracked up to be: at Brians on Purpose comes a post on how the role of mirror neurons in every aspect of human cognition has been blown out of all proportion, and from The Neurocritic is a post questioning the 'specialness' of mirror neurons, and the difference between primary motor cortex activation, and action.

- Secondly, Cgnitive Daily reviews a study on attention and intention which concludes that our conscious intentions have a greater effect on perception (and the memory thereof) than priming.

The function of the Hippocampus

In a 2004 Neuron paper, Howard Eichenbaum describes the function of the hippocampus in terms of three cognitive processes:

"The hippocampus is envisioned as critically involved in the rapid encoding of events as associations among stimulus elements and context, in the encoding of episodes as sequences of events, and in linking episodes by common features into relational networks that support flexible inferential memory expression."

There is mounting evidence for the first of these cognitive functions that the hippocampus performs which is associative representation: the encoding of "...associations among stimuli, actions, and places that compose discreet events." Functional neuroimaging studies have provided some evidence for this, however, they have also shown activation of the surrounding cortical regions - indicating that the cortex is also involved in this process of associating stimuli, albeit (perhaps) in a different manner. There has also been increasing evidence for the role of the hippocampus in learning the context of events. For example, in fear conditioning, it has been found that damage to the hippocampus results in a lack of contextual fear conditioning, without affecting the conditioned response.

The second cognitive function proposed to be mediated by the hippocampus is sequential organisation, which is "...the organisation of an episode as a sequence of events that unfolds over time." This is evidenced by the fact that damage to the hippocampus impairs order memory, bu not recognition memory. Similarly, it has been shown that it is not the relative memory trace strengths which are use to determine temporal order - and it is suggested that sequence learning is "...mediated by declarative and non-declarative strategies involving distinct memory systems, and these forms of representation are independant."

The third cognitive function is the linking of common features of disparate memory episode to create flexible representations. This is the consolidation (abstraction) of common features of different episodes into representations in their own right - the creation of semantic information from episodic memory. Further functional neuroimaging studies have shown that extensive cortical networks are activated in addition to the hippocampus when factual information is acquired. There is however a proposed difference in processing method for the two regions which facilitate this linking process: "...the hippocampus rapidly learns about individual experiences and prevents interference by separating representations of those experiences, whereas the cortex gradually extracts regularities over many experiences." This suggests a uniform underlying representation - although there would be differences based on the manner in which the memories are formed. Furthermore, it has been found that the learning of hierarchical relationships in rats is impaired by hippocampal damage. In summary, the findings suggest that while the cortex can perform complex associations, the hippocampus is required to create linkages between related memories which support inferences.

In addition to the funtional neuroimaging and behavioural evidence in support of the proposal of these three cognitive functions, the paper also reviews neural firing pattern support for these proposals, which are presented below by means of quotes of the summarising sentences.

For associative representations:

"...a prevalent property of hippocampal firing patterns involves the representation of unique associations of stimuli, their significance, specific behaviours, and the places where these events occur."

For sequential organisation:

"...the hippocampal network encodes routes through space as a meaningful sequence of events that characterise a particular spatially extended experience."

For relational networking:

"...compelling evidence for the notion that some hippocampal cells represent common features among the various episodes that could serve to link memories obtained in separate experiences."

This paper has reviewed the evidence for the proposal that the hippocampus supports three major cognitive functions. However, with this comes the acknowledgement that numerous cortical regions are also involved in these processes. Perhaps these proposals, taken with a complementary theory of cortical cognitive functioning, may be able to address some more global cognitive issues.

Eichenbaum, H. (2004). Hippocampus: cognitive processes and neural representations that underlie declarative memory. Neuron, 44(-), 109-120.