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Posts Tagged ‘arousal’

The Reticular Formation, Limbic System and Basal Ganglia

February 19, 2012 2 comments

The Reticular Formation

It’s a ‘diffuse net’ which is formed by nerve cells and fibers. It extends from the neuroaxis spinal cord through medulla, pons, midbrain, subthalamus, hypothalamus and thalamus (spinal cord is relayed superiorly to the cerebral cortex).

Many afferent and efferent pathways project in and out of the RF from most parts of the CNS. The main pathways through the RF is poorly defined and difficult to trace using silver stains. Reticular formation can be divided into three columns : median, medial and lateral columns.

Functions of the Reticular formation

1.   Control of skeletal muscles:

  • RF modulates muscle tone and reflex activities (via reticulospinal and reticulo bulbar tracts). It is important in controlling muscles of facial expression when associated with emotions.

2.   Control somatic and visceral sensation (influence can be excitatory or inhibitory)

3.   Control of autonomic nervous system

4.   Control of endocrine nervous system (hypothalamus and the pituitary)

5.   Influence on the biological clock (rhythm)

6.   The reticular activating system (arousal and level of consciousness are controlled by the RF)

Clinical note

When a person smiles for a joke, the motor control is provided by the RF on both side of the brain. The fibers from RF is separated from corticobulbar pathway (supply for facial muscles). If a patient suffers a stroke that involves corticobulbar fibers, he or she has facial paralysis on the lower part of the face, but is still able to smile symmetrically.

The Limbic System

 Limbic structures   Functions of the limbic system 
  1. Sub callosal, cingulated and parahippocampal gyri
  2. Hippocampal formation
  3. Amygdaloid nucleus
  4. Mammillary bodies
  5. Anterior thalamic nucleus
1. Influence the emotional behavior:a. Reaction to fear and angerb. Emotions associated with sexual behavior

2. Hippocampus is involved in converting short term memory to long term memory (If the hippocampus is damaged, patient is unable to store long term memory – Anterograde amnesia)

The  Basal Ganglia and their connections

Connections of the Basal Ganglia

Yellow arrow : Pallidofugal fibers

Caudate nucleus and the Putamen: main sites of receiving inputs

Globus pallidus: main site from which output leaves

Afferent and Efferent fibers

Connections of the caudate nucleus and Putamen Connections of the Globus pallidus
Afferent Efferent Afferent Efferent
CS: CorticostriateTS: Thalamostriate

NS: Nigrostriate

BS: Brainstem striatal fibers

SP: Striatopallidalfibers

SN: Striatonigral fibers

SP: Striatopallidalfibers Pallidofugalfibers

Functions of  the Basal Nuclei

Basal Nuclei controls muscular movements by influencing the cerebral cortex (it doesn’t have direct control through descending pathways to the brainstem and spinal cord). It helps to prepare for the movements (enables the trunk and limbs to be placed in appropriate positions before discrete movements of the hands and feet).

Functional connections of the Basal Nuclei and how they influence muscle activities

 
REFERENCES: 
1. Ben Greenstein, Ph.D, Adam Greenstein, BSc (Hons) Mb, ChB Color Atlas of Neuroscience
2. Allan Siegel Ph.D, Hreday N. Sapru Ph.D Essential Neuroscience, 1st Edition
3. Stanley Jacobson, Elliot M. Marcus Neuroanatomy for the Neuroscientist
4. Patrick f. Chinnery Neuroscience for Neurologists
5. Dale Purves Neuroscience, 3rd Edition
6. Suzan Standring Gray’s Anatomy
7. Keith L. Moore, Arthur F. Dalley, Anne M. R. Agur Clinically Oriented Anatomy
8. Frank H. Netter Atlas of Human Anatomy
9. Walter J. Hendelman, M.D., C.M. Atlas of Functional Neuroanatomy
10. Mark F. Bear, Barry W. Connors, Michael A. Paradiso Neuroscience Exploring the Brain
11. Dale Purves et al. Principles of Cognitive Neuroscience
12. Eric R. Kandel et al. Principles of Neural Science
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The Neuroscience of Music

February 5, 2011 Leave a comment

Why does music make us feel? On the one hand, music is a purely abstract art form, devoid of language or explicit ideas. The stories it tells are all subtlety and subtext. And yet, even though music says little, it still manages to touch us deep, to tickle some universal nerves. When listening to our favorite songs, our body betrays all the symptoms of emotional arousal. The pupils in our eyes dilate, our pulse and blood pressure rise, the electrical conductance of our skin is lowered, and the cerebellum, a brain region associated with bodily movement, becomes strangely active. Blood is even re-directed to the muscles in our legs. (Some speculate that this is why we begin tapping our feet.) In other words, sound stirs us at our biological roots. As Schopenhauer wrote, “It is we ourselves who are tortured by the strings.”

We can now begin to understand where these feelings come from, why a mass of vibrating air hurtling through space can trigger such intense states of excitement. A brand new paper in Nature Neuroscience by a team of Montreal researchers marks an important step in revealing the precise underpinnings of “the potent pleasurable stimulus” that is music. Although the study involves plenty of fancy technology, including fMRI and ligand-based positron emission tomography (PET) scanning, the experiment itself was rather straightforward. After screening 217 individuals who responded to advertisements requesting people that experience “chills to instrumental music,” the scientists narrowed down the subject pool to ten. (These were the lucky few who most reliably got chills.) The scientists then asked the subjects to bring in their playlist of favorite songs – virtually every genre was represented, from techno to tango – and played them the music while their brain activity was monitored.

Because the scientists were combining methodologies (PET and fMRI) they were able to obtain an impressively precise portrait of music in the brain. The first thing they discovered (using ligand-based PET) is that music triggers the release of dopamine in both the dorsal and ventral striatum. This isn’t particularly surprising: these regions have long been associated with the response to pleasurable stimuli. It doesn’t matter if we’re having sex or snorting cocaine or listening to Kanye: These things fill us with bliss because they tickle these cells. Happiness begins here.

The more interesting finding emerged from a close study of the timing of this response, as the scientists looked to see what was happening in the seconds before the subjects got the chills. I won’t go into the precise neural correlates – let’s just say that you should thank your right NAcc the next time you listen to your favorite song – but want to instead focus on an interesting distinction observed in the experiment:

In essence, the scientists found that our favorite moments in the music were preceeded by a prolonged increase of activity in the caudate. They call this the “anticipatory phase” and argue that the purpose of this activity is to help us predict the arrival of our favorite part:

“Immediately before the climax of emotional responses there was evidence for relatively greater dopamine activity in the caudate. This subregion of the striatum is interconnected with sensory, motor and associative regions of the brain and has been typically implicated in learning of stimulus-response associations and in mediating the reinforcing qualities of rewarding stimuli such as food.”

In other words, the abstract pitches have become a primal reward cue, the cultural equivalent of a bell that makes us drool. Here is their summary:

“The anticipatory phase, set off by temporal cues signaling that a potentially pleasurable auditory sequence is coming, can trigger expectations of euphoric emotional states and create a sense of wanting and reward prediction. This reward is entirely abstract and may involve such factors as suspended expectations and a sense of resolution. Indeed, composers and performers frequently take advantage of such phenomena, and manipulate emotional arousal by violating expectations in certain ways or by delaying the predicted outcome (for example, by inserting unexpected notes or slowing tempo) before the resolution to heighten the motivation for completion. The peak emotional response evoked by hearing the desired sequence would represent the consummatory or liking phase, representing fulfilled expectations and accurate reward prediction. We propose that each of these phases may involve dopamine release, but in different subcircuits of the striatum, which have different connectivity and functional roles.”

The question, of course, is what all these dopamine neurons are up to. What aspects of music are they responding to? And why are they so active fifteen seconds before the acoustic climax? After all, we typically associate surges of dopamine with pleasure, with the processing of actual rewards. And yet, this cluster of cells in the caudate is most active when the chills have yet to arrive, when the melodic pattern is still unresolved.

One way to answer these questions is to zoom out, to look at the music and not the neuron. While music can often seem (at least to the outsider) like a labyrinth of intricate patterns – it’s art at its most mathematical – it turns out that the most important part of every song or symphony is when the patterns break down, when the sound becomes unpredictable. If the music is too obvious, it is annoyingly boring, like an alarm clock. (Numerous studies, after all, have demonstrated that dopamine neurons quickly adapt to predictable rewards. If we know what’s going to happen next, then we don’t get excited.) This is why composers introduce the tonic note in the beginning of the song and then studiously avoid it until the end. The longer we are denied the pattern we expect, the greater the emotional release when the pattern returns, safe and sound. That is when we get the chills.

To demonstrate this psychological principle, the musicologist Leonard Meyer, in his classic  book Emotion and Meaning in Music (1956), analyzed the 5th movement of Beethoven’s String Quartet in C-sharp minor, Op. 131. Meyer wanted to show how music is defined by its flirtation with – but not submission to – our expectations of order. To prove his point, Meyer dissected fifty measures of Beethoven’s masterpiece, showing how Beethoven begins with the clear statement of a rhythmic and harmonic pattern and then, in an intricate tonal dance, carefully avoids repeating it. What Beethoven does instead is suggest variations of the pattern. He is its evasive shadow. If E major is the tonic, Beethoven will play incomplete versions of the E major chord, always careful to avoid its straight expression. He wants to preserve an element of uncertainty in his music, making our brains beg for the one chord he refuses to give us. Beethoven saves that chord for the end.

According to Meyer, it is the suspenseful tension of music (arising out of our unfulfilled expectations) that is the source of the music’s feeling. While earlier theories of music focused on the way a noise can refer to the real world of images and experiences (its “connotative” meaning), Meyer argued that the emotions we find in music come from the unfolding events of the music itself.  This “embodied meaning” arises from the patterns the symphony invokes and then ignores, from the ambiguity it creates inside its own form. “For the human mind,” Meyer writes, “such states of doubt and confusion are abhorrent. When confronted with them, the mind attempts to resolve them into clarity and certainty.” And so we wait, expectantly, for the resolution of E major, for Beethoven’s established pattern to be completed. This nervous anticipation, says Meyer, “is the whole raison d’etre of the passage, for its purpose is precisely to delay the cadence in the tonic.” The uncertainty makes the feeling – it is what triggers that surge of dopamine in the caudate, as we struggle to figure out what will happen next. And so our neurons search for the undulating order, trying to make sense of this flurry of pitches. We can predict some of the notes, but we can’t predict them all, and that is what keeps us listening, waiting expectantly for our reward, for the errant pattern to be completed. Music is a form whose meaning depends upon its violation.