
## Introduction

Moved by a professional curiosity and a growing desire to specialize in this fascinating field, I've recently completed these three neuroscience courses offered by Harvard University through the HarvardX platform:
- [Fundamentals of Neuroscience, Part 1: The Electrical Properties of the Neuron](https://www.edx.org/learn/neuroscience/harvard-university-fundamentals-of-neuroscience-part-1-the-electrical-properties-of-the-neuron?index=product&objectID=course-f8042b37-6a21-4afa-b9e2-6f51dcd694db&webview=false&campaign=Fundamentals+of+Neuroscience%2C+Part+1%3A+The+Electrical+Properties+of+the+Neuron&source=edX&product_category=course&placement_url=https%3A%2F%2Fwww.edx.org%2Flearn%2Fneuroscience)
- [Fundamentals of Neuroscience, Part 2: Neurons and Networks](https://www.edx.org/learn/neuroscience/harvard-university-fundamentals-of-neuroscience-part-2-neurons-and-networks?index=product&objectID=course-f3ec0b52-25b8-4f44-a960-e553167fd200&webview=false&campaign=Fundamentals+of+Neuroscience%2C+Part+2%3A+Neurons+and+Networks&source=edX&product_category=course&placement_url=https%3A%2F%2Fwww.edx.org%2Flearn%2Fneuroscience)
- [Fundamentals of Neuroscience, Part 3: The Brain](https://www.edx.org/learn/neuroscience/harvard-university-fundamentals-of-neuroscience-part-3-the-brain?index=product&objectID=course-70f0c8ed-1644-4c67-a5d9-7111368b4f5f&webview=false&campaign=Fundamentals+of+Neuroscience%2C+Part+3%3A+The+Brain&source=edX&product_category=course&placement_url=https%3A%2F%2Fwww.edx.org%2Flearn%2Fneuroscience)

As someone with a background in pure computer science and AI, I found myself increasingly drawn to the complexities of the human brain and its perfect engineering.

In this article, I aim not only to summarize what I've learned but also to share my unique perspective as a computer scientist. The connection between neuroscience and computer science is profound, particularly in the realms of artificial intelligence and neural networks. Neuroscience seeks to understand how the brain's network of neurons gives rise to thoughts, emotions, and behavior, while computer science has leveraged these insights to develop computational models, such as **artificial neural networks**, which mimic the structure and functioning of the human brain to solve complex problems.

## Syllabus of the Harvard courses
- Part 1: The Electrical Properties of the Neuron
  - The Resting Potential
  - Passive Membrane Properties
  - Action Potentials
  - Action Potential Propagation
- Part 2: Neurons and Networks
  - The Synapse
  - Excitation & Inhibition
  - Small Circuits
  - Neuromodulation
  - Potentiation & Depression
- Part 3: The Brain
  - Vision
  - Audition
  - Smell, Taste, and the Remaining Senses
  - Movement and Action
  - Subcortical Brain Areas

## Courses review

### Part 1: The Electrical Properties of the Neuron

**Electricity** flows in our brain, powering thoughts and actions through the movement of ions across neurons. These tiny **voltage differences**, created by ions passing through membrane channels, are the essence of neural communication. Driven by **diffusion** and **electrostatic forces**, these ions maintain a delicate balance, calculated using the **Nernst** and **GHK equations**. At the heart of this process, the **sodium/potassium ATPase pump** ensures that neurons are ready to fire, maintaining the precise ion concentrations needed for our brain to function.

<img src="/images-0002/electricity.jpeg" alt="Electricity" width="400"/>

The same principles you might learn in an Electronics course apply to how our brain works. Just as in electrical circuits, neurons rely on key concepts like **resistance** (the opposition to current flow in the membrane and cytoplasm) and **capacitance**, the ability of the membrane to store charge. These properties, governed by **Ohm’s Law**, are crucial for understanding how neurons transmit and receive signals, much like the components in any electrical system.

<img src="/images-0002/ohms-law.png" alt="Ohm's law" width="400"/>

Neurons communicate with each other using rapid changes in their membrane potentials. The **action potential** is the key electrical signal neurons use to transmit information. This all-or-nothing signal involves dramatic and rapid changes in membrane potential. The phases of an action potential are: **resting phase**, **stimulation**, **rising phase**, **falling phase**, **undershoot** and **recovery**. 

<table>
  <tr>
    <td><img src="/images-0002/resting.png" alt="Resting"/></td>
    <td><img src="/images-0002/rising.png" alt="Rising"/></td>
  </tr>
  <tr>
    <td><img src="/images-0002/falling.png" alt="Falling"/></td>
    <td><img src="/images-0002/undershoot.png" alt="Undershoot"/></td>
  </tr>
  <tr>
    <td><img src="/images-0002/recovery.png" alt="Recovery"/></td>
  </tr>
</table>

Unlike the flow of current in wires, where electrons move down the wire, in the nervous system it is the **state of depolarization** that propagates. Propagating the state of depolarization means that, even if there is no net movement of ions toward the axon, the signal arrives to the target. It's exactly what happens with waves in water. An action potential in one patch of membrane depolarizes the next region, which in turn fires an action potential. This in turn depolarizes the next region, which also fires an action potential. The process continues like a chain reaction.

### Part 2: Neurons and Networks

The junctions between neurons, called **synapses**, allow information to pass from one neuron to another. The majority of neurons are **polarized** cells. That is, they have one portion of the cell for receiving inputs and another portion for sending outputs. There are two general types of synapses:
- **electrical synapses:** few in human body, they are fast, allow synchronicity between cells;
- **chemicals synapses:** majority of connections in the human body. The propagated action potential causes a chemical to be released.

In general, the response of the postsynaptic neuron is termed a **postsynaptic potential**, and it can be: 
- **excitatory:** the neuron is more likely to fire, because it's closer to threshold;
- **inhibitory**: the received signal makes the neuron less likely to fire.

Excitation and inhibition play a crucial role in the proper function of the central and peripheral nervous system. The remarkable thing about the nervous system is the fact that the delicate excitation-inhibition balance can be achieved with a small number of **neurotransmitters** and ions but a vast diversity of **postsynaptic receptors** and specific synaptic connections.

Our nervous system, and particularly the brain, works because neurons don't live and act in isolation, but rather, they're highly interconnected in **circuits**. Each neuron within a circuit has to filter and integrate all the incoming inputs and decide whether or not to send a message down its axon. There are at least five critical factors that regulate the interaction of synaptic inputs and their ability to initiate an action potential in a target neuron:
- distance;
- non-linear summation;
- inhibitory inputs blocking excitatory inputs;
- temporal summation;
- inhibitory inputs blocking temporal summation.

**Neuromodulation** is the process by which the synaptic transmission between two neurons is either enhanced or decreased through the action of a third substance called **neuromodulator**. Neuromodulators can act on synapses in a variety of ways, both pre and post synaptically, affecting neurotransmitter release, receptor sensitivity, as well as downstream gene expression and protein synthesis. The main neuromodulatory systems are: 
- serotonine;
- neuropeptides; 
- dopamine; 
- acetylcholine;
- noradrenaline.

Neuronal circuits are plastic: they are able to change in response to numerous internal and external stimuli. In other words, they are shaped by experience. This phenomenon is called **neuronal plasticity**. Neuronal plasticity happens all the time in our brain. For example, your brain is changing as you read these lines. 

### Part 3: The Brain

#### Vision

The visual system is the part of the central nervous system that gives organisms the ability to detect, process, and interpret information from **visible light** with the goal of building a representation of the surrounding environment. The process begins with the reception of light and processing of such input in each of our eyes by a special structure called the **retina**. Information is then transmitted along the **optic nerve** into a relay station deep within the brain called the **thalamus**, where inputs are sorted and begin to be processed. From there, this information goes to the visual cortex.
<img src="/images-0002/vision.png" alt="Vision" width="400"/>

#### Audition

Sound is produced when something **vibrates**, causing variations in the medium pressure around it. In order to hear, our ears must capture the mechanical energy of sound waves, efficiently transmit that energy to receptors, and those receptors must translate that energy into a code that's useful for neurons, namely into electrical signals. These three processes are carried out by three structural components of the ear, the **outer ear**, the **middle ear**, and the **inner ear**.
<img src="/images-0002/audition.png" alt="Audition" width="400"/>

I won’t delve into the details of vision and audition, nor our other senses and their connection to the brain, even though this is one of the most fascinating parts.

#### Movement
The **spinal cord** generates **motor action** all by itself. Motor inputs coming from the brain, however, significantly alter and control the movements.
<img src="/images-0002/motor.png" alt="Brain control of movement" width="400"/>

#### Subcortical brain areas

<table>
  <tr>
    <th style={{ width: '20%' }}>Brain area</th>
    <th style={{ width: '35%' }}>Where is it</th>
    <th style={{ width: '50%' }}>What it does</th>
  </tr>
  <tr>
    <td>**The Hindbrain**</td>
    <td><img src="/images-0002/hindbrain.png" alt="The Hindbrain" width="200"/></td>
    <td style={{ borderBottom: '1px solid black' }} >The hindbrain is a collection of structures that are responsible for many of our **autonomic functions**. It consists of the **brainstem** (medulla, pons, and **midbrain**) and the **cerebellum**. It controls essential functions like breathing, digestion, regulation of sleep, heart rate and blood pressure, swallowing, chewing, facial expression and upright posture. It also controls **protective motor reflexes**, like those that cause vomiting, coughing, sneezing. </td>
  </tr>
  <tr>
    <td>**The Midbrain**</td>
    <td><img src="/images-0002/midbrain.webp" alt="The Midbrain" width="200"/></td>
    <td style={{ borderBottom: '1px solid black' }} >Sitting at the center of the brain, the midbrain is associated with **vision**, **hearing**, and **motor control**. It's also associated with the **regulation of sleep** and wake cycle, arousal and alertness, and **temperature** regulation. It contains the **substantia nigra** a small brain region that synthesize **dopamine**, a neurotransmitter tied to **motivation**.</td>
  </tr>
  <tr>
    <td>**The Cerebellum**</td>
    <td><img src="/images-0002/cerebellum.png" alt="The Cerebellum" width="200"/></td>
    <td style={{ borderBottom: '1px solid black' }} >The cerebellum play a key role in **motor programming** although it doesn't generate motor activity itself. As such the cerebellum is thought to be a major facilitator of **motor learning**. More recently scientists have discovered a key role for the cerebellum in certain **cognitive functions** like language.</td>
  </tr>
  <tr>
    <td>**The Forebrain**</td>
    <td><img src="/images-0002/forebrain.png" alt="The Forebrain" width="200"/></td>
    <td style={{ borderBottom: '1px solid black' }} >The forebrain is the largest division of the brain and remains the most glamorous and complex in its function. Broadly, the forebrain encompasses four main functional systems: the **cerebral cortex**, the **basal ganglia**, the **thalamus** and the **limbic system**.</td>
  </tr>
  <tr>
    <td>**The Basal Ganglia**</td>
    <td><img src="/images-0002/basal-ganglia.png" alt="The Basal Ganglia" width="200"/></td>
    <td style={{borderBottom: '1px solid black'}}>The basal ganglia is deeply interconnected with the neocortex, brainstem, and thalamus, among other brain areas. Functionally, the basal ganglia is associated with **voluntary movement**. It's also involved in the **learning** and **execution** of **actions** that become **habitual** or **automatic**. More recently, scientists have recognized the basal ganglia also plays a key role in **emotional and cognitive functions**. A number of neurological disorders are the result of damage to the basal ganglia, including **Parkinson**'s and **Huntington**'s disease.  </td>
  </tr>
  <tr>
    <td>**The Thalamus**</td>
    <td><img src="/images-0002/thalamus.png" alt="The Thalamus" width="200"/></td>
    <td style={{ borderBottom: '1px solid black' }} >The thalamus is considered to be the **relay station** of the brain. It makes reciprocal connections between both higher and lower brain areas. **Every sensory system**, with the sole exception of the olfactory system, **sends its input to cortex through** a specific **thalamic nucleus**.</td>
  </tr>
  <tr>
    <td>**The Limbic System**</td>
    <td><img src="/images-0002/limbic-system.png" alt="The Limbic System" width="200"/></td>
    <td style={{ borderBottom: '1px solid black' }} >The **amygdala**, one particular area of the limbic system, is especially important for processing **memories** that have **emotional significance** and making decisions based on those memories. Many of these regions are involved in recognizing **rewards** and reinforcements, threats and **punishments**.</td>
  </tr>
  <tr>
    <td>**The Hippocampus**</td>
    <td><img src="/images-0002/hippocampus.png" alt="The Hippocampus" width="200"/></td>
    <td style={{borderBottom: '1px solid black'}}>Two major roles of the hippocampus are in **declarative memory consolidation** (the recall of stored facts and experiences) and **spatial navigation**. The hippocampus is one of only two regions where **neurogenesis**, the birth and migration of new neurons, has been found to occur in the adult brain.</td>
  </tr>
  <tr>
    <td>**The Hypothalamus**</td>
    <td><img src="/images-0002/hypothalamus.png" alt="The Hypothalamus" width="200"/></td>
    <td style={{ borderBottom: '1px solid black' }} >Certain parameters such as **temperature** or **glucose** levels must be held constant. This is known as **homeostasis**. If any parameters deviate from the optimal set point, it’s the job of the hypothalamus to bring the body back to normal activating the **autonomic nervous system**, the **endocrine system** and rhe **behavioral system**.</td>
  </tr>
</table>

## Connecting the dots: from the brain to AI

Something that I found particularly intriguing is the concept of **nonlinear summation of excitatory postsynaptic potentials (EPSPs)**. In the brain, when two EPSPs occur close together in time or space, their combined effect is not merely additive. Instead, the interaction between them can amplify or diminish the overall signal in a nonlinear manner. This phenomenon parallels the way **weights** in **deep neural networks** function. In a deep learning model, the weights assigned to inputs are not simply combined in a straightforward manner but are processed through **activation functions**, which introduce nonlinearity. This nonlinearity allows the network to model **complex** relationships within data, much like how the brain's nonlinear summation enables sophisticated neural processing.
<table>
<tr>
    <th style={{ width: '50%' }}>EPSPs summation</th>
    <th style={{ width: '50%' }}>DNN</th>
  </tr>
  <tr>
    <td><img src="/images-0002/summation.png" alt="Non linear summation"/></td>
    <td><img src="/images-0002/dnn.png" alt="Deep Neural Network"/></td>
  </tr>
</table>
Considering the scenario of the experiment represented in the picture on the left, what we observe is that:
- when we stimulate the blue and green electrodes separately we'll have two EPSPs of the **same amplitude**
- when we stimulate them at the same time the resulting EPSP is bigger than the single one but **smaller than the sum of the two**. The summation is not linear.

Additionally, I was struck by the similarity between the **ventral visual pathway** in the brain and **convolutional neural networks (CNNs)** used in computer vision. The ventral pathway processes visual information hierarchically, from detecting simple features like **edges** and **lines** to recognizing complex objects such as **faces**. Similarly, CNNs are structured in layers, where each successive layer extracts more complex and abstract features from the input image. Early layers might detect edges, while deeper layers identify patterns and shapes, culminating in the recognition of entire objects. The similarity between the ventral pathway and CNNs is not surprising. CNNs are inspired by the brain’s functioning, as reflected in their very name.
<table>
<tr>
    <th style={{ width: '50%' }}>Ventral pathway</th>
    <th style={{ width: '50%' }}>CNNs</th>
  </tr>
  <tr>
    <td><img src="/images-0002/ventral-pathway.jpeg" alt="Ventral Pathway"/></td>
    <td><img src="/images-0002/cnn.png" alt="Convolutional Neural Network"/></td>
  </tr>
</table>

## Conclusion

This course provided me with a solid understanding of the fundamentals of brain and nervous system function. I find the intersection between AI and the human brain particularly fascinating. AI is inspired by the brain, and conversely, AI serves as a powerful tool to deepen our understanding of the brain's complexities. My professional motivation lies in exploring how AI can help us better understand the human brain. In conclusion, this course introduced me to several intriguing subjects like **optogenetics** (a biological technique to control the activity of neurons or other cell types with light), **connectomics** (the study of the connections in the nervous system), and the **Csikszentmihalyi's flow model** (next picture), all of which triggered my curiosity.
<img src="/images-0002/flow-model.png" alt="Csikszentmihalyi's flow model" width="400"/>

## Useful links

- [Introduction to neural networks](https://medium.com/@theDrewDag/introduction-to-neural-networks-weights-biases-and-activation-270ebf2545aa)
- [Convolutional Neural Network](https://poloclub.github.io/cnn-explainer/)
- [Excitatory postsynaptic responses to presynaptic impulses](https://www.sciencedirect.com/science/article/abs/pii/B9781483201030500107)
- [The ventral visual pathway](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3532569/)

During the Neuroscience classes from HarvardX, I learned that

Fundamentals of Neuroscience


The Erasmus program changed my life in ways I never expected. I want to share my story with you, hoping it will inspire you to take that leap into the unknown and embrace the world beyond your comfort zone.

## How things started

I've always been attracted to this program. The opportunity to travel, go far from home, and experience a new culture among new people felt like one of the most exciting things a young adult could do. So, in January 2022, during the final year of my university studies in Italy, I decided to take the plunge, leaving Italy for a six-months Erasmus in Paris.

## The beginning: new faces, new frienships

From the very first days in the sweet city, my life became a whirlwind of new faces and friendships. I met around 20 new international people almost instantly, not to mention those I met during classes, events, and through friends. The atmosphere was warm and welcoming, and in no time, I formed bonds that would last throughout the Erasmus program and beyond.
![Group photo](/images-0001/everyone.jpeg)

## The best part: laughter, adventures and Paris

What made the Erasmus experience so special were the laughter. From the very start, everything seemed comical in the best way possible. The food we tried, the unfamiliar smells, the unexpected, all made us laugh. Even classes, which had never felt so engaging before, took on a new level of excitement.

But the best part was the trips to Paris. We organized group outings, sometimes with way too many people, running after trains that were even more delayed than we were. Our destinations varied, but the joy was always the same. We explored Paris by day, visiting museums, parks, neighborhoods, and iconic landmarks like the Eiffel Tower and Montmartre. We had picnics everywhere. We felt like royals in Versailles and like babies in Disneyland. We scheduled volleybal matches in the golden hour. We shared lunches, dinners, barbecues. We were there for the gay parade and late-night parties.
 
It was impossible not to connect with the people around. We were all friends. A group of people protecting each other, a balance of laughter, respect, cordiality, differences, gossip, quarrels, and strong emotions. Every place was amazing. Every day, I was surprised. Each of those days was a bundle of new sensations. New ways of seeing the same world and new worlds to see.
![Pride](/images-0001/pride.jpeg)

## The end: bittersweet goodbyes

Time flew by faster than we expected. Those six months were intense, filled with almost daily adventures. It felt like I had lived three years’ worth of experiences in that short span. But as with all good things, it had to end.

June arrived without anyone noticing. The first departure made some of us cry, and others followed. We made our way to the airport to say goodbye, organizing several farewall events to close this chapter of our lives. The last parties, the last hugs. We all felt deeply emotional. We knew we were saying goodbye to something unique, something we might never find again.

My turn came. I returned to Italy by train, accompanied by two friends who would take different paths once we reached Milan. We said our goodbyes, holding on to the memories, the photos, and fading our connection on social media.

## What remains: memories that last a lifetime

Few years have passed since that experience, but those six months remain the time in my life when I felt most alive, free, and truly happy. I was exactly where I needed to be.

Looking back, I realize that the awareness of having a limited time was one of the reasons why I lived every moment as intensely as possible. I connected with people quickly and deeply because we all understood that our time together was short. And in the end, that's what life is like. One, short, made up of moments you can choose to live or to waste.

This experience has stayed with me, shaping the way I approach life, relationships, and opportunities. I hope my story encourages you to take that step, to embrace the unknown, and to create your own unforgettable memories.

![Napoli](/images-0001/naples.jpeg)
In this picture, Ilaria, Chiara and I during one of our reunions in Naples.

The Erasmus program changed my life in ways I never expected

maiorcasfolio

Fundamentals of Neuroscience

The Erasmus