The Neurobiology of Language and Memory

Notes…

 

LeDoux, Synaptic Brain

 

p303 " ...the neural mechanism underlying the perception of spatial relations is present in both hemispheres of other primates; it is mainly on the right side in humans. This implies that spacial perception was forced from the left during the language invasion of human synaptic territory."

 

What the language areas evolved from

 

(Rita Carter ‘Mapping the Mind’ Phoenix 2000 p228)

 

“The main language areas are situated in the left hemisphere of the brain, in the temporal (side) and frontal lobes. If you look down on a slice of the brain cut horizontally and at a certain level, you will see that these areas are marked by a distinct, one-sided bulge. The equivalent areas in the right hemisphere are concerned mainly with processing environmental noises and with spatial skills: the rhythm and melody of music impacts here; the ‘where’ of things in the outside world is registered and fine hand movements – including gestures (but not formal sign language) – are processed.”

 

“The region where language developed is also rich in connections to deeper brain structures that process sensory stimuli, and it is one of the places where stored impressions from different senses, particularly touch and hearing, are brought together and reassembled into coherent memories.”

 

Theory of Mind

 

(Rita Carter ‘Mapping the Mind’ Phoenix 2000 p235)

 

Rita introduces two stories, one requiring a theory of mind, the other not. “The question that called for a calculation about another person’s mental state (in this case the burglar’s false belief) lit up a spot in the middle of the prefrontal cortex… This did not happen when the subjects worked out the answer to the second question.” (Which related to why the alarm went off when the burglar stepped on a soft furry object that screeched and ran off.)

 

Memories and Meanings

 

(By Walter J Freeman in  Rita Carter ‘Mapping the Mind’ Phoenix 2000 p240)

 

“Our brains don’t take in information from the environment and store it like a camera or a tape recorder, for later retrieval. What we remember is continually being changed by new learning, when the connections between nerve cells in brains are modified.

 

A stimulus excites the sensory receptors, so that they send a message to the brain. That input triggers a reaction, by which the brain constructs a pattern of neural activity. The sensory activity that triggered the construction is then washed away, leaving only the construct. That pattern does not ‘represent’ the stimulus. It constitutes the meaning of the stimulus for the person receiving it.”

 

In other words, it is structured using the elements of the Quest, Explorer and Sentic modules, each part thus set in relation to the other players in the story in question. But maybe that is only true of one form of memory - episodic, not all.

 

Locations of memories

 

(Rita Carter ‘Mapping the Mind’ Phoenix 2000 p264)

 

Temporal Lobe: long-term memories permanently lodged in the cortex

Putamen: procedural memories, like riding a bike are stored here

Hippocampus: involved in laying down and retrieving memories, particularly personal [episodic] ones, and those relating to finding your way about [right side only].

Amygdala: unconscious traumatic memories may be stored here.

Caudate nucleus: many instincts – which are genetically encoded memories – stem from here.

 

Working Memory

 

(Rita Carter ‘Mapping the Mind’ Phoenix 2000 p308)

 

Professor Alan Baddeley, of Bristol University, has developed a model of working memory based on three parts:

 

The Central Executive – co-ordinates information from a number of sources, directs the ability to focus and switch attention, organises incoming material and the retrieval of old memories and combines information arriving via two temporary storage systems:

 

Visuo-spatial sketch pad holds images

 

Phonological loop holds acoustic and speech-based information

 

Brain imaging studies at the Wellcome Department of Cognitive Neurology have found that the three parts are echoed precisely in the activity seen when people carry out cognitive tasks.”

 

Baddeley says “We believe that the phonological loop can be split into two components: a memory store that holds a fast-decaying (one to two seconds) speech-based trace, and a rehearsal system that repeats the trace and registers it in the memory store via non-vocalised speech. Hence a visually presented set of letters can be remembered by saying it to oneself. But because the memory trace fades while the rehearsal is going on we can typically only remember as many words as we can say in two seconds.” …

“Less is known about the more complex visuo-spatial sketch pad although the four active regions so far identified by functional imaging are thought to represent ‘what’, ‘where’, executive control and possibly image rehearsal.”

 

(Rita Carter ‘Mapping the Mind’ Phoenix 2000 p312)

 

“The nuts and bolts of thinking – holding ideas in mind and manipulating them – takes place in a region of cortex on the dorsolateral (upper side) prefrontal cortex. This is also the location of the closely related activity called working memory [executive function?]. Planning takes place in this area, and it is here that choices are made between various possible actions. Some studies suggest that each type of information has its own special temporary storage niche. An area in the upper reaches of the right hemisphere prefrontal lobe, for example, has been found to light up when a person holds information about objects that are temporarily out of sight. Another spot nearby seems to hold the memory of how many times you have done a thing before. … The essential requirement for following through a plan is to put aside things that are immediately attractive in favour of those that further long term strategy. This ability seems to be located in the orbital-frontal cortex – the region that lies behind the bridge of the nose and continues beneath the bottom curve of the brain, running backwards towards its core.”

 

“…the basic drives, urges and desires that motivate behaviour come from the unconscious brain and are essentially reflexive: automatic responses to environmental stimuli. If you see food, for example, and your hypothalamus is registering hunger, your unconscious brain prompts you to eat it. …”

 

“The orbito-frontal cortex has rich neural connections to the unconscious brain where drives and emotions are generated. The down signals from the cortex inhibit reflex clutching and grabbing, and if you take away that control – as happens sometimes in  frontal lobe injury – the unconscious retakes the body. This is seen in a bizarre condition called magnetic apraxia. Patients with this disorder automatically scan the environment for anything that catches their attention. When something does, they reach out and grasp it. Sometimes they are unable to let go.”

 

Meaning

 

(Rita Carter ‘Mapping the Mind’ Phoenix 2000 p320)

 

“Its [consciousness's] most important component is not the ability to plan, or choose, of follow through a strategy despite the insistent urgings of our unconscious brain to chase each passing shadow. Rather it is the intuitive sense of meaning that binds our perceptions into a seamless whole and makes sense of our existence.

Can that , too, be pinpointed?

Astonishingly, it seems that it can. Meaningfulness is inextricably bound up with emotion. Depression is marked by wide ranging symptoms but the cardinal feature of it is the draining of meaning from life. People in a severe state of depression fail to see life as a unified pattern and start instead to see it as a fragmented, incomprehensible sequence of pointless events. Social bonds are severed, normal activities seem purposeless – everything seems to be falling apart. By contrast, those in a state of mania see life as a gloriously ordered, integrated whole. Everything seems to be connected to everything else and the smallest events seem to be bathed in meaning. A person in this state is euphoric, full of energy and flowing with love. They are also in a high state of creativity – the connections they see between things, which are often invisible or overlooked by others, are often used by them to make new concepts.

The area of the brain which is most noticeably affected in both depression and mania is an area on the lower part of the prefrontal cortex – the ventromedial or subgenual cortex. This as we have seen is the brain’s emotional control centre. It is exceptionally active during bouts of mania, and inactive (along with other prefrontal areas) during depression. The connections between this region and the limbic system beneath it are very dense, closely binding the conscious mind with the unconscious, and this configurement is probably what gives it its special status: it is, if you like, the part that best incorporates the whole of our being, making sense of our perceptions and binding them into a seamless whole.”